diff --git a/pkg_resources/__init__.py b/pkg_resources/__init__.py
index c86d9f095cc..647654fbb14 100644
--- a/pkg_resources/__init__.py
+++ b/pkg_resources/__init__.py
@@ -36,7 +36,6 @@
     MutableSequence,
     NamedTuple,
     NoReturn,
-    Sequence,
     Set,
     Tuple,
     Type,
@@ -49,6 +48,7 @@
     Iterable,
     Optional,
     TypeVar,
+    overload,
 )
 import zipfile
 import zipimport
@@ -99,7 +99,7 @@
 from pkg_resources.extern.platformdirs import user_cache_dir as _user_cache_dir
 
 if TYPE_CHECKING:
-    from _typeshed import StrPath
+    from _typeshed import StrPath, StrOrBytesPath, BytesPath
 
 warnings.warn(
     "pkg_resources is deprecated as an API. "
@@ -1041,7 +1041,7 @@ class Environment:
 
     def __init__(
         self,
-        search_path: Optional[Sequence[str]] = None,
+        search_path: Optional[Iterable[str]] = None,
         platform: Optional[str] = get_supported_platform(),
         python: Optional[str] = PY_MAJOR,
     ):
@@ -1084,7 +1084,7 @@ def remove(self, dist: "Distribution"):
         """Remove `dist` from the environment"""
         self._distmap[dist.key].remove(dist)
 
-    def scan(self, search_path: Optional[Sequence[str]] = None):
+    def scan(self, search_path: Optional[Iterable[str]] = None):
         """Scan `search_path` for distributions usable in this environment
 
         Any distributions found are added to the environment.
@@ -1288,7 +1288,7 @@ def extraction_error(self) -> NoReturn:
         err.original_error = old_exc
         raise err
 
-    def get_cache_path(self, archive_name: str, names: Iterable[str] = ()):
+    def get_cache_path(self, archive_name: str, names: Iterable["StrPath"] = ()):
         """Return absolute location in cache for `archive_name` and `names`
 
         The parent directory of the resulting path will be created if it does
@@ -1340,7 +1340,7 @@ def _warn_unsafe_extraction_path(path):
             ).format(**locals())
             warnings.warn(msg, UserWarning)
 
-    def postprocess(self, tempname: str, filename: str):
+    def postprocess(self, tempname: "StrOrBytesPath", filename: "StrOrBytesPath"):
         """Perform any platform-specific postprocessing of `tempname`
 
         This is where Mac header rewrites should be done; other platforms don't
@@ -2465,12 +2465,16 @@ def null_ns_handler(
 register_namespace_handler(object, null_ns_handler)
 
 
-def normalize_path(filename: "StrPath"):
+@overload
+def normalize_path(filename: "StrPath") -> str: ...
+@overload
+def normalize_path(filename: "BytesPath") -> bytes: ...
+def normalize_path(filename: "StrOrBytesPath"):
     """Normalize a file/dir name for comparison purposes"""
     return os.path.normcase(os.path.realpath(os.path.normpath(_cygwin_patch(filename))))
 
 
-def _cygwin_patch(filename: "StrPath"):  # pragma: nocover
+def _cygwin_patch(filename: "StrOrBytesPath"):  # pragma: nocover
     """
     Contrary to POSIX 2008, on Cygwin, getcwd (3) contains
     symlink components. Using
@@ -2481,9 +2485,19 @@ def _cygwin_patch(filename: "StrPath"):  # pragma: nocover
     return os.path.abspath(filename) if sys.platform == 'cygwin' else filename
 
 
-@functools.lru_cache(maxsize=None)
-def _normalize_cached(filename):
-    return normalize_path(filename)
+if TYPE_CHECKING:
+    # https://github.com/python/mypy/issues/16261
+    # https://github.com/python/typeshed/issues/6347
+    @overload
+    def _normalize_cached(filename: "StrPath") -> str: ...
+    @overload
+    def _normalize_cached(filename: "BytesPath") -> bytes: ...
+    def _normalize_cached(filename: "StrOrBytesPath") -> Union[str, bytes]: ...
+else:
+
+    @functools.lru_cache(maxsize=None)
+    def _normalize_cached(filename):
+        return normalize_path(filename)
 
 
 def _is_egg_path(path):
@@ -2736,7 +2750,7 @@ def __init__(
     def from_location(
         cls,
         location: str,
-        basename: str,
+        basename: StrPath,
         metadata: _MetadataType = None,
         **kw: int,  # We could set `precedence` explicitly, but keeping this as `**kw` for full backwards and subclassing compatibility
     ):
@@ -2996,7 +3010,7 @@ def __dir__(self):
     @classmethod
     def from_filename(
         cls,
-        filename: str,
+        filename: "StrPath",
         metadata: _MetadataType = None,
         **kw: int,  # We could set `precedence` explicitly, but keeping this as `**kw` for full backwards and subclassing compatibility
     ):
@@ -3332,7 +3346,7 @@ def _find_adapter(registry: Mapping[type, _AdapterType], ob: object):
     raise TypeError(f"Could not find adapter for {registry} and {ob}")
 
 
-def ensure_directory(path: str):
+def ensure_directory(path: "StrOrBytesPath"):
     """Ensure that the parent directory of `path` exists"""
     dirname = os.path.dirname(path)
     os.makedirs(dirname, exist_ok=True)
diff --git a/setuptools/build_meta.py b/setuptools/build_meta.py
index 5799c06ed63..91c176b47e5 100644
--- a/setuptools/build_meta.py
+++ b/setuptools/build_meta.py
@@ -36,12 +36,13 @@
 import tempfile
 import warnings
 from pathlib import Path
-from typing import Dict, Iterator, List, Optional, Union
+from typing import Dict, Iterator, List, Optional, Tuple, Union
+from collections.abc import Iterable
 
 import setuptools
 import distutils
 from . import errors
-from ._path import same_path
+from ._path import same_path, StrPath
 from ._reqs import parse_strings
 from .warnings import SetuptoolsDeprecationWarning
 from distutils.util import strtobool
@@ -113,7 +114,7 @@ def _get_immediate_subdirectories(a_dir):
     ]
 
 
-def _file_with_extension(directory, extension):
+def _file_with_extension(directory: StrPath, extension: Union[str, Tuple[str, ...]]):
     matching = (f for f in os.listdir(directory) if f.endswith(extension))
     try:
         (file,) = matching
@@ -370,11 +371,11 @@ def prepare_metadata_for_build_wheel(
 
     def _build_with_temp_dir(
         self,
-        setup_command,
-        result_extension,
-        result_directory,
-        config_settings,
-        arbitrary_args=(),
+        setup_command: Iterable[str],
+        result_extension: Union[str, Tuple[str, ...]],
+        result_directory: StrPath,
+        config_settings: _ConfigSettings,
+        arbitrary_args: Iterable[str] = (),
     ):
         result_directory = os.path.abspath(result_directory)
 
@@ -404,7 +405,10 @@ def _build_with_temp_dir(
         return result_basename
 
     def build_wheel(
-        self, wheel_directory, config_settings=None, metadata_directory=None
+        self,
+        wheel_directory: StrPath,
+        config_settings: _ConfigSettings = None,
+        metadata_directory: Optional[StrPath] = None,
     ):
         with suppress_known_deprecation():
             return self._build_with_temp_dir(
@@ -415,12 +419,16 @@ def build_wheel(
                 self._arbitrary_args(config_settings),
             )
 
-    def build_sdist(self, sdist_directory, config_settings=None):
+    def build_sdist(
+        self, sdist_directory: StrPath, config_settings: _ConfigSettings = None
+    ):
         return self._build_with_temp_dir(
             ['sdist', '--formats', 'gztar'], '.tar.gz', sdist_directory, config_settings
         )
 
-    def _get_dist_info_dir(self, metadata_directory: Optional[str]) -> Optional[str]:
+    def _get_dist_info_dir(
+        self, metadata_directory: Optional[StrPath]
+    ) -> Optional[str]:
         if not metadata_directory:
             return None
         dist_info_candidates = list(Path(metadata_directory).glob("*.dist-info"))
@@ -433,7 +441,10 @@ def _get_dist_info_dir(self, metadata_directory: Optional[str]) -> Optional[str]
         # get_requires_for_build_editable
         # prepare_metadata_for_build_editable
         def build_editable(
-            self, wheel_directory, config_settings=None, metadata_directory=None
+            self,
+            wheel_directory: StrPath,
+            config_settings: _ConfigSettings = None,
+            metadata_directory: Optional[str] = None,
         ):
             # XXX can or should we hide our editable_wheel command normally?
             info_dir = self._get_dist_info_dir(metadata_directory)
diff --git a/setuptools/command/install_lib.py b/setuptools/command/install_lib.py
index 32ff65e783b..9d76e429e82 100644
--- a/setuptools/command/install_lib.py
+++ b/setuptools/command/install_lib.py
@@ -2,6 +2,7 @@
 import sys
 from itertools import product, starmap
 import distutils.command.install_lib as orig
+from .._path import StrPath
 
 
 class install_lib(orig.install_lib):
@@ -85,8 +86,8 @@ def _gen_exclusion_paths():
 
     def copy_tree(
         self,
-        infile,
-        outfile,
+        infile: StrPath,
+        outfile: str,
         preserve_mode=1,
         preserve_times=1,
         preserve_symlinks=0,
@@ -96,7 +97,7 @@ def copy_tree(
         exclude = self.get_exclusions()
 
         if not exclude:
-            return orig.install_lib.copy_tree(self, infile, outfile)
+            return orig.install_lib.copy_tree(self, infile, outfile)  # type: ignore[arg-type] # Fixed upstream
 
         # Exclude namespace package __init__.py* files from the output
 
diff --git a/setuptools/command/install_scripts.py b/setuptools/command/install_scripts.py
index d79a4ab7b03..e9b0a0fe022 100644
--- a/setuptools/command/install_scripts.py
+++ b/setuptools/command/install_scripts.py
@@ -2,6 +2,7 @@
 import distutils.command.install_scripts as orig
 import os
 import sys
+from typing import List
 
 from .._path import ensure_directory
 
@@ -13,12 +14,12 @@ def initialize_options(self):
         orig.install_scripts.initialize_options(self)
         self.no_ep = False
 
-    def run(self):
+    def run(self) -> None:
         self.run_command("egg_info")
         if self.distribution.scripts:
             orig.install_scripts.run(self)  # run first to set up self.outfiles
         else:
-            self.outfiles = []
+            self.outfiles: List[str] = []
         if self.no_ep:
             # don't install entry point scripts into .egg file!
             return
diff --git a/setuptools/config/expand.py b/setuptools/config/expand.py
index 0d8d58add82..3dc156a8d7f 100644
--- a/setuptools/config/expand.py
+++ b/setuptools/config/expand.py
@@ -119,7 +119,9 @@ def glob_relative(
     return expanded_values
 
 
-def read_files(filepaths: Union[str, bytes, Iterable[StrPath]], root_dir=None) -> str:
+def read_files(
+    filepaths: Union[StrPath, Iterable[StrPath]], root_dir: Optional[StrPath] = None
+) -> str:
     """Return the content of the files concatenated using ``\n`` as str
 
     This function is sandboxed and won't reach anything outside ``root_dir``