Failure to reconnect to networks on iOS
Things to try... is the same behavior observed if you:

borrow an iDevice (running iOS 14) from someone else and connect it to your network
temporarily disable MAC filtering and/or the hidden attribute of your wireless network

(I’ve made the assumption that you’ve already re-booted both your iOS device and the Airport Extreme, and that they both have the most current software.)
As a last resort (that won’t cause you to lose any data, but that will delete any saved WiFi passwords not saved to iCloud - maybe turn off iCloud first just to be safe):

Use the “Reset Network Settings” option under Settings &gt; General &gt; Reset


While not the issue in your case, others may encounter a similar issue with the ‘private address’ feature in iOS 14, on a network has MAC filtering enabled.

When connected to your network, does “Privacy Warning” appear under the network name on the Wi-Fi settings?
If not, click the info circle to the right of the network name, then toggle off the “Private Address” option, which by default in iOS 14 assigns a new MAC address to your device on a regular basis (each time? every day?)