I've found a simple workaround, not perfect but it's been enough to restore my productivity for the time being.
The second solution in this post is simple to do and worked. It's reverting to an older version of office, without copilot.
Remove Copilot from Word - Microsoft Community
I've copied the text across.
"We recommend that you restore your Microsoft 365 version to a earlier version, see the following:
Restore your version of Office
- Close all Office software, in the "Start Menu", find "Command Prompt" (or "cmd"), right-click and select "Run as administrator" ;
- At the command prompt, type the following command and press Enter*:*
cd %programfiles% \Common Files\microsoft shared\ClickToRun
- Then enter the following and press Enter
Officec2rclient.exe /update user updatetoversion=16.0.17531.20120
This will bring Office back to a stable version in February 2024.
If the above steps are successful, you'll be able to view Office version 17531.20120 under File -> Account -> Product Information. If another version is displayed here, it means that some of the steps were not executed successfully, please refer to the previous method and try again.
After restoring, open any Office application, such as Word, click File -> account. On the right side, check the "Microsoft 365 and Office Updates" heading , click the "Update Options" button, and select the "Disable Updates" option to disable the auto-update feature."
The first time I did this, it failed. Although I had closed all my office programs, I still had Edge open because I was following the instructions. I copied the instructions across to the very non-Microsoft Scrivener, closed Edge and repeated the procedure and it worked.
It's not ideal, as I'm now paying for old software I can't update, but at least I can work. I'm hoping that Microsoft are a bit more responsive than they were about the issue with never combining taskbar buttons. They did fix it eventually, and I was finally able to buy a new computer which ran Windows 11, but it took two years of numerous people giving them feedback that they wanted this option back.