Hi, this is my first post here so sorry if I do something wrong, I have a Xiaomi r4ac or 4A, the Chinese version and 100m, my issue is that I tried to install openwrt and I actually succeeded, but the 5Ghz was not working at all, so I tried to fix it and eventually I just went back to Xiaomi firmware, but now 5Ghz is not working anymore, I think it is because before installing openwrt I had a higher version, but now I can not find nothing above 2.18.58, so my question is
if someone has the same router and, by any chance, you made a backup of the original firmware, can you upload it? thanks 
You had to back upnsystem calibration partition. Those data can not be recovered from thin air. As for 100M - you can buy gigabit routers for 20 bucks nowadays.