I have an EdgeRouter12 (ER-12) which doesn’t appear on the supported hardware lists. I considered picking firmware meant for similar hardware with a MIPS64 chip but as the box is still sealed I think i’m better off selling it.
Devices OpenWRT recommends: https://openwrt.org/toh/views/toh_available_864
Devices OpenWRT supports: https://openwrt.org/toh/start
OpenWRT does support a lot of Ubiquiti hardware though: https://openwrt.org/toh/start?dataflt[Brand*~]=Ubiquiti
I found an old D-Link DIR-885L and gave it new life instead: OpenWRT general guide / D-Link DIR-885L