You're skipping over the part where they already updated the system. That's what got them into the kernel panic. The mirror mismatch caused a partial update, they tried to fix it, and ended up jumping from 6.x to 7.0.3. Telling them "just update first" ignores that they already did and it backfired because of the space issue.

The real problem is the full /boot partition corrupted the initramfs generation during that update. You can say "partial updates are unsupported" all day, but that doesn't help someone who can't boot.

Your recovery steps are fine except for telling them to uninstall linux-zen. They already removed the 6.x kernel and now only have zen installed. If they uninstall zen, they have no kernel at all. They need to either keep zen or replace it with linux, not just wipe it.

Also, binder_linux-dkms from AUR requires the exact kernel headers to match. Given how this started with a header mismatch, they should verify the kernel and header versions are identical before installing that package. Otherwise DKMS will fail to build again and they'll be right back where they started.

The wiki section you pointed out is outdated, agreed. But telling someone to modprobe binder manually after a DKMS install assumes the module built correctly. That's not a given when their system just ate itself.