Updated to 14.1 (and since that time to 14.2) and my phone frequently can't use WiFi anymore. I have to toggle WiFi off, then use phone's data, to access pages. I can use WiFi on some, but frequently hit "Safari cannot access ... no server." I then toggle off WiFi. I have been turning WiFi off and on now for days. It is SOOOOO irritating. It is also very very slow now operating. The update to 14.2 took 27 minutes!!! I only did it hoping Apple had fixed Wifi problem. But it hasn't. I took off Privacy setting on my home network, I rebooted home modem/router, I removed home network from phone and reconnected, and I deleted History/cache of Safari. I am not going to do an entire factory reset. But this is HORRIBLE that I can't use my own Wifi network reliably anymore and have to use my phone's cellular data.
IOS 14 update and WiFi problems on iPhone XI
Same problem on all iOS14.x devices https://developer.apple.com/forums/thread/651079?page=1#654065022
Had the same issues but it was finally solved when I did a complete reset of my network settings.