Thank you S.Sengupta for your comment.
Unfortunately, I already tried all, and it didn't work.
BUT
I solved my problem. Here's how.
Some days ago, while still struggling with the problem, I remembered that some days before the beginning of my issues I "freed up" space occupied by OneDrive files: I opened Windows explorer --> went to OneDrive folder --> right clicked on the folder --> from the context menu I clicked "Free up space", to remove files from my local drive and leave all online.
While removing the files, windows notified me that some files were system files or locked, but I didn't think much about it.
The following days I began having problems with the taskbar icons but didn't relate the situation to my action on OneDrive.
Two days ago I had a revelation.
I then opened OneDrive folder, searched inside for the Documents folder, right-clicked the Documents folder, and chose "Always keep on this device". OneDrive synched the files and downloaded the online files to my local drive ... and booom!
My icons came back almost suddenly.
Since then I have had no more issues.
Hopes this can help
Regards
Paolo