Problem
Several users in a account with multiple Google Workspace Editions are unable to edit and collaborate on files stored in Shared Drives. Users are only able to view the files.
Solution
It is expected for users with subscription that do not support Shared Drives not to be able to edit, or manage files in a Shared Drive. Such users have 'Viewer', access to the files.
Users with unsupported subscriptions can be added directly on the individual file permission rather than the overall Shared Drive, this will enable the user to Edit that document.
The help center article here talks about the limitations expected for Admins and users.