Learn the basics of GPT and MBR:
- Back up every partition (XFS => xfsdump).
- Enable UEFI Secure Boot in BIOS and disable MBR protection in BIOS. Disable CSM and hybrid mode (UEFI + CSM) in BIOS.
- Wipe every MBR partition table and create a fresh new GPT partition table.
# cfdisk --zero /dev/sda
=> gpt
- Fill the new GPT partition table with partitions.
I recommend cfdisk for all partition table work.
# cfdisk /dev/sda
- Restore backup (XFS => xfsrestore). Fill the new partitions with data from backup.