I have an iPad Air 3rd Gen and an iPhone 11 that had issues after updating to iOS 14.1. After several attempts to Join my network, I received a cryptic message to the effect that iOS didn't like being assigned a static IP address. This didn't make sense as I have a lot of iOS devices on my network and they are all assigned static IP addresses. I was using MAC Filtering on my router to whitelist the devices that could log in so I checked the MAC addresses on the problematic devices against those in the whitelist and everything matched. Out of frustration, I disabled MAC Filtering on my router, an Viola! All the devices where able to Join! My router is a Linksys EA9500. Hope this helps.

I finally figured out what was going on with my network connection and MAC address filtering on my router. There is apparently a new feature in IOS 14 called PRIVATE ADDRESS. It is found under Settings -> WI-FI -> <Your Network Name>. This setting can be turned ON and OFF and assigns a unique MAC ADDRESS for your device on a particular network that is independent of the hardware Wi-Fi MAC address found under Settings -> General -> About -> Wi-Fi Address. Private Address is supposed to limit how your device can be tracked across networks. I tuned OFF Private Address for all devices on my home network and turned MAC Filtering back ON in my router and now everything appears to working as before. I know this may not solve your particular issue, but it's something to be aware of. I knew nothing of this new feature until I started poking around in Settings trying to get some more clues about what was going on in my particular scenario. The problem with this feature (in my case) is that it is ON by default and apparently active when you get the HELLO / Set-up screen in IOS. I had this situation after the upgrade to IOS 14, so no matter what I did, I could not sign into my home network during the upgrade and log into iCloud. As I mentioned, this is probably not related to the larger issue being discussed on this forum, but I wanted to share this information for those who might be curious. Have a nice day.