The discussion of power supplies made me wonder if that was the problem I was having with my Holife wireless charger - although I was already using an Apple 5W brick that many seem to be finding success with. I’d previously used this to charge my iPhone 8 just fine, but the 12 wasn’t having it. Last night I tried using an old Apple 10W brick (from an iPad 2 iirc) and that seems to have done the trick.
Now, this could be a case of user error, as I just checked the underside on the Holife and it does say “5V 2A input” which I had apparently not been providing. Still, it had been working fine with the 8, and as it didn’t come with a brick of its own that implied to me that any standard USB supply ought to work. I’d be interested to hear if anyone else finds this to be the problem.