If you are unsure, go with UCRT64.
The MSYS environment contains the unix-like/cygwin based tools, lives under /usr and is special in that it is always active. All the other environments inherit from the MSYS environment and add various things on top of it.
this doc contains how to configure terminal.integrated.profiles in VSC
pacman -Ss gcc # search gcc online
pacman -Qs gcc # search gcc in local
pacman -Ss gcc | grep ucrt # filter ucrt
pacman -Qs gcc | grep ucrt # filter ucrt pwd | xargs.exe cygpath.exe -m {} # get pwd and convert to windows paths