openbsd.txt

download the arm64 install75.img file:
https://www.openbsd.org/faq/faq4.html#Download

use balena etcher to flash install75.img to MicroSD

UART connection to RPi

GND to pin 6, black wire
RPi TX to pin 8 (laptop receives data from RPi over this line), white wire
RPi RX to pin 10 (laptop sends data to RPi over this line), green wire

minicom -s
serial port setup

A - serial device = /dev/ttyUSB0 (for me)
E - Bps/Par/Bits = 115200 8N1
F - hardware flow control = no (TX from laptop to RPi won't work if this is wrong)
G - software flow control = no (probably also important)
(press enter to exit that screen)
select Exit to finish setup and go to main minicom screen


there's openbsd info here but it was TMI for me
https://ftp.openbsd.org/pub/OpenBSD/7.5/arm64/INSTALL.arm64
https://www.openbsd.org/faq/faq4.html#Install