How I can hide Delete permanently option from dropdown under deleted files section in files
If you only want to hide the button, you can use the Custom CSS app. Unfortunately, I can’t give you any specific code. Maybe someone here can help. But there are certainly examples on the internet.
Personally, I see no reason for your action. Normally you make a daily backup of Nextcloud. This means that files should only be lost if you create and delete the file on the same day. That should be acceptable.