Seeing as I started this thread, I had better finish it 
I’ve been out of town for two weeks so I’ve only just had a chance to try out the tin foil hack. It took me about four attempts yesterday with different thicknesses of foil to get the oven to stay on and connected for more than 30 minutes. Eventually I got there and I left the oven on overnight last night.
This morning: success! the oven UI had a clock, and it now works properly. The UI shows I’m on the latest firmware. So I guess the foil hack works, and thankfully I do not have to return my oven (which is apparently mandatory for us here in Canada - do ask, as I was properly annoyed by that)
I do have another issue, which I have worked around. I was unable to get my oven to connect to my app, but I think it’s related to WPA3 security on my Eero Wifi Router.
Anyway, after 4 weeks with a bricked oven, I now have my (kitchen) right hand back.