Hi @Anonymous ,
Could you please share a bit more about your issue?
Do you mean that you do not permission to edit the field properties within the form you created?
Based on the issue that you mentioned, I have made a test on my side, and don't have the issue that you mentioned. Please check if you have been assigned with proper Security Role in current PowerApps Environment.
Please go to Power Platform Admin Center, then find your current Eivonment in Environment tab, then click "Settings", then expand the "Users + Permissions" option, then click "Users", within the opening Users page, find your account, select it then click "Manage Roles" option in top menu, then check if you have been assigned with "System Administrator" Security Role.

If you have been assigned with the "System Administrator" Security Role in current environment, but the issue still exists, please check if you have owned proper PowerApps license for your sign in account or your PowerApps license has been expired.
Note: Currently, if you want to access Model-Driven App functionality or CDS functionality in PowerApps, you must own PowerApps Plan 1 license at least. Office 365 license is not allowed to access CDS functionality in PowerApps.
Please consider take a try with above solution, check if the issue is solved.
Best regards,