@woozle Thanx! For anyone with the same problem. I confirm that https://forum.openwrt.org/t/porting-firmware-to-tp-link-archer-c20-v5/35512/85 provided the solution. I just flashed the provided...

I have flashed the latest OpenWrt successfully, yet the performance is underwhelming due to the lack of hardware offloading. I would like to flash the stock, yet the normal TFTP recovery doesn't work...