I have since discovered that two apps Start11 and Explorer Patcher work great together. Problem with opening the Registry and trying to export a key only happens when both apps are installed and only after I run Disk Cleanup.
Yes, I have Registry pinned to both Start11 and the standard Start Menu in Windows 11. Some type of temp file gets removed during the disk cleanup process when both apps are installed.
In this case, I opted to uninstall Start11 until this glitch is fixed. I do like Start11 a lot and want to reinstall it.