Hey,
I've spent the last few days setting up 64-bit Archlinux (AArch64) on my Raspberry Pi 4 Model B with Full USB Boot (no SD card necessary), Encryption for the root filesystem as well as using btrfs as the root filesystem.
Putting it all together took quite some effort, and I decided to put together a comprehensive step-by-step guide on how to get there, including the EEPROM update.
You can find the guide here: https://gist.github.com/XSystem252/d274 ... 0d59647928
I hope this will prove helpful to some.
Cheers
XSystem