What is more reliable for daily backup, rsync or Time Machine?

Time Machine in macOS Big Sur, when set up with an APFS volume, uses a completely different system for keeping your versions separated and organized.

If you are using Big Sur, I strongly recommend this approach. Use Disk Utility to make sure your disk is formatted with APFS then add it to Time Machine. Your backups will now appear as “volumes” inside the disk and can be browsed easily with Finder or with Time Machine’s custom UI.