Seem to have resolved the wi-fi issue!! It took a long time on the phone with Apple Support (who were actually pretty good despite having to go through many of the steps again that I had already tried).
Basically it came down to having to plug my new iPhone into my MacBook Pro via USB-C and doing a full reset that then automatically updated the iPhone to iOS 17.1.1. I then had to start the 'transfer' process again from my old iPhone 12 Pro and somehow it seems to now connect to my home wifi OK.
I did get caught in a bit of a 'loop' where the reset was asking me to turn off 'Find Me' which I couldn't do as it required my Apple ID and password and of course I wasn't connected to wi-fi so it wouldn't work!! I'm really sorry but I can't recall how that was finally resolved as I'd been on the phone a couple of hours by then and all a little muddled...suffice it to say that little issue did resolve itself and all looking good so far.
Apologies for forgetting the fix for turning off 'Find Me' but Apple Support may help you if you are experiencing a similar problem during the reset and new transfer process.
Hope that is at least useful to some and shows the issue can be resolved...I was also close to just returning the new iPhone if it hadn't worked too!