Serial Console & TTYs
assuming you have a apu2|apu3|apu4 from pcengines or a virtual machine running on KVM/Qemu. And you don’t have vga/dvi/hdmi whatever kind of video output. of course, you can install and run OpenBSD (or Linux) on this boxes.
Prepare USB Stick
write openbsdxx.img to an USB Stick. On MacOS, you can use Balena Etcher for example.
boot.conf
if you wanna install from an USB Stick, set the correct Port and Speed before booting.