iOS 14 Can No Longer See AirPort Express in AirPlay Device List

Try to reinstall 14.4.2 if possible and then power off and restart the entire network.....all devices. You may need to Erase All Content and Settings on the iOS device and then restore it from a backup.

If you are still having problems, you have an iOS issue, not an AirPort issue. Nothing changed on the AirPort. Please post over in the iOS support forum linked below for more help.

Using iPhone

Since updating to iOS 14. 4 I can no longer see my AirPort Express that is joined to my main wireless network....

Not an AirPort Express issue......(nothing changed on the AirPort Express).....it is an iOS issue. Welcome to the iOS 14.4 club, where Apple broke things that were working fine before. Not all users are affected of course, but we have seen any number of posts about this issue. There are no sure fire solutions.

So that we don't waste your time asking you to perform troubleshooting steps that you have already done, could you please list the actions that you have already tried?

Edit to post above........which mentions that you are using iOS 14.4. If you have not already done so, download and install 14.4.1.

Did you install the iOS update 14.4.1? The information in your post indicates that you are using 14.4.

14.4.2 and airport has dropped off again.