v1.21 was released a couple days ago. I just tested it and the problem
has been solved. It also works without the need for a serial console.
The whole thing can be done from keyboard+monitor console. This may have
been possible in a few previous versions, but I never bothered testing it.
I can confirm that as of at least v1.21 no serial console is necessary.
Follow the directions up to the point of seeing the UEFI screen. From
Device Manager -> Raspberry Pi Configuration -> Advanced Configuration:
Limit RAM to 3 GB: Disabled (OpenBSD doesn't need this)
System Table Connection: ACPI + Devicetree
Save, Esc back to top, reset, enjoy (or curse at the next problem that
I have seen no difference between "Devicetree" and "ACPI + Devicetree",
but "ACPI" without devicetree will fail. I grabbed a dmesg from
both and did a diff. The only difference was memory usage. Someone
smarter that I might confirm if ACPI is needed at all.