This comprehensive guide outlines the exact, step-by-step procedure to manually roll back an Arch Linux system utilizing systemd-boot, Unified Kernel Images (UKI), Btrfs subvolumes, and Snapper when the system is unbootable, followed by fixing the missing kernel modules and broken Snapper bindings entirely offline.
When your system is completely broken or stuck on a black screen, you cannot use automated tools. You must boot into any Arch Linux Live USB and manually swap the subvolumes using the Btrfs command-line tools.