If desktop environment or display manager fails to start or shows black screen, you need to use TTY to access your system to fix something.
If your system fails to boot, you need to use a Live USB to arch-chroot to your broken system and then fix something for example: Reinstall or downgrade Kernel, repair bootloader or remove bad kernel modules, etc… except complete corrupted filesystem and hardware failure.
You need to prepare a good backup solution before corrupted filesystem or hardware failure.
There are many different backup programs: https://wiki.archlinux.org/title/Synchronization_and_backup_programs
Restoring a snapshot or backup will help you after accidentally deleting data or recursively change data by your mistake.
Do not forget to enable REISUB that ist useful for safe shutdown when your computer freezes.