Hi Moshe. I'm Greg, an installation specialist, 10 years awarded Windows MVP, and Volunteer Moderator. If you will work with me I will be here to help until the issue is resolved.
- See if you can System Restore to a point before the problem began following this guide: https://www.windowscentral.com/how-use-system-r...
- The closest there is to resetting This PC in Navigation Pane to default is to try removing This PC from the Navigation Pane in File Explorer, then restart PC and add it back again. See here:
https://www.tenforums.com/tutorials/5352-add-re...
- There are also these registry edits for removing items from Navigation Pane which may be helpful in trying to sort this out:
https://www.askvg.com/windows-10-tip-remove-one...
Unfortunately this is all there is as of now on editing Nav Pane. I hope it's helpful.
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Linked tutorials are from trusted Microsoft MVP's.