You could try changing the Wi-Fi name and password of the Swisscom router to the same as the Unifi ap and then unplug the Unifi ap. Then connect the TV box to the Swisscom router, unplug the TV box, switch off the WLAN of the Swisscom router again and switch on the Unifi ap again. Then the Swisscom TV box should connect to the ap. Can't guarantee that it will work. Greetings Nils and please tell me if it works.

The Ubiquti AP provides its own WLAN - if the Swisscom box can be used as a "modem", then UNIFI can provide the WLAN. In my opinion, no other variant works (although I am not a mega-specialist either).