@David-TP yes, turning off v1 devices allowed the firmware to be installed and ethernet backhaul now works for guest wifi.

@David-TP Experiencing this issue with main deco M9plus v2.2 on 1.9.1 build 20250612 rel 45960 and three satellites M9plus v1 on 1.7.1 build 20250905 rel. 58382. I tried to install the firmware...