I'm trying to do the same thing that @EconomiCurtis was trying to do that @mine answered in Sharing an RStudio.Cloud Project, and Copying the Project to Convert it from Temporary to Saved
I.e., add students as Viewers (not contributors) to a posit.cloud project, where they can start an assignment and save a permanent copy.
I don't have the permanent save option. This is what the menu bar looks like for my "student test account"
Compare to the one from @mine in the original post:
In case anyone wants to join the project to test here's the invite link