SAVED FOR FUTURE REFERENCE https://apple.stackexchange.com/a/359056/457053

The Disk Utility application probably can not be use to fix your Mac. Below is a alternate procedure.

Start up the Mac from macOS Recovery over the Internet by restarting and immediately pressing and holding the the key combination Option-⌘-R.
From the menu bar, select to open a Terminal application window.

Enter the following command to get the GUID Partition Table (GPT) entries.

$ gpt -r show disk0

An example output is shown below.

$ gpt -r show disk0
      start       size  index  contents
          0          1         PMBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6         
         40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640   97656248      2  GPT part - FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF
   98065888        544         
   98066432   97245184      3  GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
  195311616        891         
  195312507         32         Sec GPT table
  195312539          1         Sec GPT header

Enter the command given below to change the GPT.

gpt -f remove -i 3 disk0
gpt -f remove -i 2 disk0
gpt -f add -i 2 -b  <start> -s <size> -t apfs disk0

Where <start> and <size> are integers taken from the row with index equal to 2 in the table shown in step 2. An example is shown below.

$ gpt -f remove -i 3 disk0
disk0s3 removed
$ gpt -f remove -i 2 disk0
disk0s2 removed
$ gpt -f add -i 2 -b  409640 -s 97656248 -t apfs disk0  
disk0s2 added

You will need to replace 409640 and 97656248 with the values shown in your GPT table.

Restart the Mac back to macOS Mojave.

Enter the command given below in a Terminal application window to reclaim the free space.

$ sudo diskutil apfs resizeContainer disk0s2 0