The problem: When I share a Win10 computer with my son, I need to prevent accidental deletions of my files.

— Idea (unsuitable): The folder security/permission system is over-complicated and poorly documented.
— Idea: right-click -> properties -> hidden -> only the folder (excluding subfolders)
I can verify that in my son’s mswe, this folder is effectively hidden 🙂
— idea (surprise 🙂 msfe->GiveAccessTo->RemoveAccess
GiveAccessTo is designed for NETWORK sharing, but with this set-up I was able to limit access by my son’s account 🙂

Tested 5 times on c:\0, c:\0x, c:\0dummy folders.
— idea: EFS i.e. windows Encr Filesystem
Encrypted files can still be deleted, according to some site, but I’m not convinced.

How to remove encryption? FileOnwership -> Personal?

When you encrypt a file or folder with EFS, a new entry, ‘File ownership’, appears in the context menu of the file or folder to make it easier to decrypt.