Hi Tom
Like you i was getting frustrated, and although i was given lots of advice none of it seemed to work, and some seemed very complicated to do. So i consulted Microsoft and the agent’s advice was to do a clean install of Windows which need not affect your files or apps. It would lead to a clean uptodate copy with any corrupted or missing files sorted out. The agent took over my PC and showed me how it was done. You simply go to the MS website and look for the version of W11 you want - home/pro etc. within an hour or so the problem was solved. The worst part was the queue waiting for an agent to come free. I would recommend it if you are struggling.
Mike