I have been trying to get AArch64 to run on a new Pi-64GB for a few months now.
After first trying to do my standard configuration (root on a btrfs partition on an external SSD) I was surprised by several errors.
So I tried to run the minimal configuration.
That is - the pure installation as it is described in the wiki.
This resulted in the following error message during boot:
Raspberry OS 86Bit & 64Bit work without problems - only Arch64 does not want to work.
I also set root= in boot.txt to mmcblk1p2 (and of course ran mkscr afterwards) but that didn't improve anything either.