I tried creating a MS-DOS(FAT) partition and the operation failed. Here's the stuff from "Show details"
Running operation 1 of 2: Add “Untitled” by splitting “Macintosh HD”…
Resizing APFS Container designated by APFS Container Reference disk1
Verifying storage system
Using live mode.
Performing fsck_apfs -n -x -l /dev/disk0s2
Checking volume.
Checking the container superblock.
Checking the EFI jumpstart record.
Checking the space manager.
Checking the object map.
Checking the APFS volume superblock.
Checking the object map.
Checking the fsroot tree.
Checking the snapshot metadata tree.
Checking the extent ref tree.
Checking the snapshots.
Checking the APFS volume superblock.
Checking the object map.
Checking the fsroot tree.
Checking the snapshot metadata tree.
Checking the extent ref tree.
Checking the snapshots.
Checking the APFS volume superblock.
Checking the object map.
Checking the fsroot tree.
Checking the snapshot metadata tree.
Checking the extent ref tree.
Checking the snapshots.
Checking the APFS volume superblock.
Checking the object map.
Checking the fsroot tree.
Checking the snapshot metadata tree.
Checking the extent ref tree.
Checking the snapshots.
Verifying allocated space.
warning: Overallocation Detected on Main device: (1891539+39) bitmap address (3969378)
The volume /dev/disk0s2 appears to be OK.
Storage system check exit code is 0.
Shrinking APFS Physical Store disk0s2 from 250,790,436,864 to 125,395,218,432 bytes
Shrinking APFS data structures
APFS Container Resize error code is 49168
A problem occurred while resizing APFS Container structures.
Operation failed…