Prioritise connection (wifi / ethernet)

Given that the siren is rubbish, as it is so quiet no-one externally would notice and someone internal could just unplug it, we are forced to find a more difficult location to place the homebase. That tends to be away from the ethernet. I have therefore bought a sim router plugged in via ethernet and have WiFi as backup (I think, it says if ‘unplugged’ it’ll switch). I would like to prioritise wifi, but cant. In any case, I would like to have both wifi and 4g for Resilience and would want to prioritise faster wifi.