This file just to be clear:
https://downloads.openwrt.org/releases/23.05.3/targets/ath79/generic/openwrt-23.05.3-ath79-generic-watchguard_ap300-squashfs-factory.bin
There are a number of different WG firmware versions I've seen and they appear differently, espcially the very early ones. But all have accepted that upgrade and ended up booting openwrt.