@annetoal
Let me suggest a couple of options.
You might consider the in-place records management feature available in SharePoint. Allow your users to upload edit etc. After the document has been approved you can declare it as a record - this can be done with Flow. Once it is a record it cannot be edited or deleted regardless of your permissions.
Another option is to use a second library. Allow your users edit permissions there. Once the document is approved, move it to the primary library using Flow. The primary library can be locked down so that your users cannot edit, delete, etc..
Finally, if you want to use a "for a selected document" Flow, you'll need to be using the modern interface.