I have successfully built app-backup/borgbackup on arm64 and used it to restore backed up files. I think the ebuild should support arm64 officially.
Here is the list of rules I added to accept_keywords:
Steps to Reproduce:
1. Add ** keywords for various components (see above)
2. emerge app-backup/borgbackup
3. Run borg
Thank you for the report! We're already on it in bug 766525 but I've had some hardware issues recently :|
*** This bug has been marked as a duplicate of bug 766525 ***