MacOS GPT Messed up File System ('FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF')

Solution 1:

The first partition (the EFI partition) is mislocated. It should start at block 40 and end at block 409639 (=moved by 6 blocks towards the end of the disk).

In Recovery Mode you can simply remove the first partition and add it again properly aligned:

gpt remove -i 1 /dev/disk0
gpt add -i 1 -b 40 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B disk0

This apparently(?) solved the problem and the Mac booted again properly.

To verify the integrity of the APFS container afterwards enter:

diskutil list #to get the device number of the APFS container scheme device (probably disk1)
diskutil verifyVolume disk1

The result should be: Storage system check exit code is 0!