@RicardoATB I'm using the 2020 firmware. I hope the new one (from 2021) will fix the issue as it has ADDED MESH functionality : Release note for the 2021 firmware:

Hi, I have one root AP (EAP660 HD), and I bought an EAP620 V2 to run as a wireless mesh AP to extend my WiFi coverage. The EP620 shows "CONNECTED" as mesh when I use am Ethermet cable running from it...