I can change the interface priority here. But it seems to take a long time and maybe a reboot. Is there a fast way to change it on the device?
Can you ssh into the Pi/host?
If so, then sylvain.goyette might suggest using
ifmetric wlan0 500
ifmetric wwan0 300
or some such metrics … per his post : [SOLVED] Lower priority of wwan0 over eth0