System restore on Windows not working due to an error referring to a Dropbox folder

I need to restore my system due to a problem with my Windows/Fonts folder.

However, whenever I try to run System Restore, after about 20 minutes Windows restarts with the following error message:
https://www.dropbox.com/scl/fi/8cs9ufypm9f2ntom1jvin/temp-1.png?rlkey=ny26ffpl7ssueq13h1lh67duz&st=wzq01mjv&dl=0

(I tried posting the above url as a link but I got a message saying that the link contained invalid html! But I didn't write any html, I just used the Insert Link button. Why doesn't the Insert Link button create links that can be posted?)

As the error message was referring to a Dropbox folder, and I don't need Dropbox to be restored, I need my Fonts folder to be restored, I tried uninstalling the Dropbox desktop app for Windows and running System Restore again - but I got the same error message.

I then tried deleting the Dropbox folder from my hard drive, and running System Restore again - but I still got the same error message.

So how can I restore my syste?

I have a hunch that the problem might be somehow related to the fact that I upgraded Dropbox for Windows at the time of the last automatic restore point. But how can I get round it?

It is extremely serious if the Dropbox upgrade has somehow made it impossible to run System Restore. How can I fix this?   

Dave