No permission "Edit form layouts" (greyed) for Custom Managers

Hello, we have a custom Manager’s Permission Role where the users are restricted to see only they assigned projects.

We are not able to activate the permission “Edit form layouts” for standard entity creation (project, shot, asset or task).
The checkbox remains greyed and display the message/tip :
“When checked, users can modify and save the layout of entity creation forms. This permission is disabled for this permission group, to enable please turn off “See Assigned Projects Only” advanced permission.”

I found this odd that the feature to cutomize layout is dependant to the acces to all Projets.

Has anyone been able to find a way to activate this permission ?