Ok, so this is embarrassing. My password manager (I blame a piece of software, obviously) made a practical joke, providing the wrong wifi password
Wifi is now working just fine.
Thanks for all your help and suggestions, it definitely made me a bit more knowledgeable, if nothing else!
Now I’m off to start a new thread about “why does the emoncms db on my emonpi not import historical data from my iotawatt, while my other RPI with my own emoncms db setup does?”