Yeah, I realized that after posting but I couldn't move it and didn't want to delete it.
Anyway I managed to convert router to openwrt. As I done it, I will briefly describe process. While flashing firmware my router was mesh node in xiaomi mesh.
I used this patcher to gain ssh access to router. Permanent access is also available.
In ~/.ssh/ create file named config and add to it
HostKeyAlgorithms = +ssh-rsa
PubkeyAcceptedAlgorithms = +ssh-rsa
After that you can ssh root@router_ip. Password is root.
I grabed firmware from this github repo. On the bottom of the page there are instructions in
Use miwifi (the vendor firmware) to flash
I tried to wget or curl this image from the router but no success. It will download empty file. I download it to my computer and done
scp *.ubi root@192.168.31.145:/tmp
Firmware is now copied to router /tmp directory. In that directory check curremt system slot like described in firmware repo and just run ubiformat on another slot.
Also after flashing run nvram commands and reboot router.
And that was it. Openwrt is installed on AX3000 RA80 Chinese model.
The only thing I noticed so far is that I get empty 5Ghz wifi on scanning but maybe some additional config should be used.