iPhone 7Plus not connecting to WIFI

Hi team!

My iPhone has taken on a chronic issue of not connecting to any WIFI. I have tried various different routers at different sites and the problem persists. I have a back up iPhone with me that is connecting to the same WIFI routers so I can confirm the issue is not the network but definitely the iPhone. However, the back-up does not have all my Apple IDs set up or half the functionality of this newer iPhone and I do not wish to transfer my data or apps to it (it is just for emergencies and booking local taxis etc.).

I have read through and acted upon the troubleshooting page If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network and have even gone through the 'Reset Network Settings' option a couple of times, switched the device off/ on several times and tinkered with just about every possible setting that I can find.

The iPhone is finding the servers/ routers and the WIFI icon flashes up for a few seconds but then it just reads 'No Internet Connection'. What's going on with it, and is there any way to remedy this issue?

Maybe someone has a tip for fixing this?

I would attempt to run an update of the software (I'm currently on 15.1) but, obviously, I would need an internet connection to achieve that. Maybe I can plug the device into my Mac and access WIFI that way?

Many thanks in advance,

Adam