Current release (7.7) and previous (7.6) worked great on my Pi 4. There were a few extra setup steps due to the unique firmware boot setup, but after it works exactly like any other OpenBSD system. I rarely think about it being ARM64.

Runs great even in a passive enclosure. It's gotten it quite hot before when left it running in a backpack by mistake... but it remained perfectly stable and I could SSH into it (though I didn't dare touch it).

https://www.openbsd.org/arm64.html