I have two different devices, one running OpenWRT 19.07.8 and one running OpenWRT 21.02.2.
My device running OpenWRT 19.07.8 has a wireguard interface, it connects the tunnel directly not matter if wan or wwan0 interface has a working connection to the endpoint.
The other device running OpenWRT 21.02.2 only establish the wireguard interface it it has a connection over wan. Even if I have wwan0 and can ping the endpoint or manually create a route to the endpoint on wwan0 the wireguard interface does not even show up ?
Is it a bug or has something else changed that I am not aware of - I have tried using option tunlink 'wwan0' but it does not change anything.
I have the same issue on a Turris Mox: did you find a solution to make wireguard connect on wwan like it does on wan?
Now I am running 21.02.3 and suddenly the problem was solved, I have had it once more on another device:-(
But after a while it started to work, during one setup when I had the problem I named the interfaces inet_a and inet_b just to see if that solved my problem - but it was something else, unfortunately I cant explain it
Thanks for your feedback.
For now, my workaround has been to put another device in front of it, that connects to the wifi, and is plugged with ethernet on the WAN plug. So it "forwards" the internet access to my Turris, that sees is as its WAN.