ALFA Network AC1200R is not supported by OpenWrt due to its unsupported Lexra SoC.
See https://openwrt.org/docs/techref/hardware/soc/soc.realtek#lexra for more details.
SoCs of the Lexra Architecture are not supported by OpenWrt since years. It is unlikely that this status changes anytime soon.
IMHO: There are better ways to waste your time than trying to get a current OpenWrt running on a Lexra device.