I want to collaborate on a project with people, but there are some files in my project that I do not want them to be able to edit. I think it would be great to have a menu for each file where you can set up specific permissions for different people that you are collaborating with so that you can make some things unreadable, like your .env file, or uneditable. My vision is pretty much the permissions options of Google Docs. This would be useful if you want to keep some of your code private or make a file where your collaborators can code, and a final file for only the code that you approve.
This suggestion is like this one, however specific to files rather than an entire project.