Unable to boot into Mac OSX after updating dual-boot Ubuntu, Partition Type FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF
Usually when the FFFFFFFF-FFFF-FFFF-FFFFFFFFFFFF error occurs, the partition starting and ending values are still correct. I assume this is true in your case. If I am correct, then you need to enter the following commands to change FFFFFFFF-FFFF-FFFF-FFFFFFFFFFFF to 7C3457EF-0000-11AA-AA11-00306543ECAC.

diskutil unmountdisk disk0
gpt remove -i 2 disk0
diskutil unmountdisk disk0
gpt add -i 2 -b 409640 -s 1900925984 -t apfs disk0


The EFI partition (disk0s1) is used occasionally by macOS, so you need to keep this partition. However, Grub files were added to this partition when you installed Ubuntu. The commands below will remove any Grub files that may still exist on the EFI partition . You can enter these commands while booted to macOS.

sudo diskutil mount disk0s1
cd /Volumes/EFI/EFI
rm -rf BOOT
rm -rf ubuntu
cd ~
diskutil unmount disk0s1


To add the free space back to macOS, enter the command given below. You can enter this command while booted to macOS.

sudo diskutil apfs resizeContainer disk0s2 0