Just ran into this with 5.4.4 and an already installed and working Xcode and wanted to share the fix I did. It seems the paths were not lining up with what UE expected. (This is possibly because I had updated Xcode without opening it to accepts all the settings/license stuff.) As a result, even after getting Xcode back to normal, UE still could not find it. The fix is to make Xcode reset all the paths by running:
sudo xcode-select -r
NOTE: since these tools are controlled by root, you need to do this with sudo.
Hope this helps.