Cannot run anything as administrator

Actually, I may have been too hasty here! Although it fixed the current machine I am using, I went to another PC I have which has EXACTLY THE SAME Windows 11 22H2 version and build, and there is nothing wrong with "Run As Administrator" or anything else on the context menus (using the new style contracted menu). The PC I had trouble with is the only one experiencing these problems, so my guess now is that your first observation may be correct (NCH software is causing the problem). I only uninstalled the "Express Zip File Compression" program, so now I will revert to the "compact" content menus, uninstall ALL NCH programs (5 of them) and reboot to see if that was the problem. If it fails, at least I have the option of reverting to the full context menu.
I had updated to W11 22H2 via inline System Update (through an ISO) rather than waiting for Microsoft to update via the normal process. All other computers are updated except the one I am having trouble with. I guess it was not updating because of the problem I am experiencing.
Maybe If I had simply uninstalled all the NCH programs and then attempted a normal update it would have worked, so the "NCH" problem may in fact stop PCs from updating to 22H2 Build!
(If I paid money for NCH programs I want my money back!)