I got some free stuff someone was getting rid of. A TP Link AC 1900 C9, and a SmartRG sr400ac. It seems like openwrt has a target file for the sr400ac, but there does not seem to be official pages or talk about installing it. I am guessing the factory OS flash updater isn't going to like that file, but maybe. Have not tried. Was asking here first.
OK guys no one said anything and it was a free stuff of the internet item, so I used the existing os flasher and the file appearing the 21.02.00 targets. It seemed I had to do a factory restore sort of reset later as it did not respond to 192.168.1.1 initially. It did so afterwards though and it working fine so far.