I've been trying to look for a solution to this issue for the past few days, it's been a challenge, lol!!
@AndreasSta I tried what you suggested about Creating a Solution, Adding your desktop flow to it then Exporting it as a Managed Solution.
I uploaded the new Solution in a different Environment and indeed the "Edit", "Create a Copy" and "Share" feature were all disabled as shown in the picture 1 below.

However, when I go into the Power Automate Portal (https://make.powerautomate.com/), creating a copy through the "Save as" feature is still available!! (picture 2)

I tried a few things but nothing seems to fully solve the issue.
Did you experience the same difficulty??
@agadari
I also tried your suggestion on copying the "Basic user" security role and restricting "Create" and "Write" privileges in the Process table.
I even tried to disabled all the "Create" and "Write" permissions, but the "Save as" option to create a copy is still showing up!
Can you please share a bit more on how you did it?