Sounds like some file system problem.
Did you just update something?
How long since reboot?
Just putting some questions out there.
Not an MS person, so I can't recommend a file system checker.
Someone else might know.

Good luck.

I did reboot first thing. No recent update, but auto updates is on. Maybe I should delete last update?

Pretty sure it's an issue at MS, not me. Word is still fine.

I did a quick web search, and it could be that anti-virus is playing games.

https://spreadsheetplanet.com/remove-read-only-from-excel/
https://support.microsoft.com/en-us/office/why-did-my-file-open-read-only-3ab4b792-da50-4b38-8628-14c64e1f1d15

Doubtful that you messed up a setting (accidentally) to save files as read-only.
https://www.exceldemy.com/excel-this-workbook-was-opened-in-read-only-mode/

But people accidentally change settings. I do, and make a good (unpaid) living here at DU helping people figure out that they did, how, and how to undo. (iphones make private mode too easy to set).

HTH

AVG suddenly decided to block Excel files - all on its own!

WTF?!

Thanks!

Super glad that it worked out for you!!!!

thanks!

And select 'Open as Administrator". If this is not in your context menu, try 'Take ownership' and see if that makes a difference.

There has just been a windows update. I haven't seen any ill-effects (yet).

To do a file system check follow these steps:

1. Open My Computer window.
2. RIGHT click on the C drive and select Properties
3. The resulting window will have several tabs. Select the Tools tab
4. First object is Error Checking. Click on CHECK
5. You may get a message that you don't need to check the drive. Don't matter, do it anyway.

Most times, you can get it to check while still using the computer but you also may need to 'Schedule a file check' for the next reboot.

Thanks!

Listen here...I trialed my suspicion and it allowed me to save to OneDrive but not to my PC - as I've always done!

I will try your solution next - thanks!

I realize that I've applied a tweak to 'Take Ownership', so you may not see it. But....here's a link to a trusted source for the tweak.

https://www.majorgeeks.com/content/page/take_full_ownership_of_files_folders.html

On this page they show three ways of adding Take Ownership to your context menu. The first and second ways are extremely easy and they both work.

But I just read your post again and think it may be the new Microsoft AI BS. It's called Copilot. You may have to search for it in Settings so you can turn it off. Have you seen an indication that it's on your computer? It arrived on mine several days ago.

It changed a setting...blocking Excel files! I've reset it. Argh!