Microsoft recently released a new feature to "Block unmanaged customizations (Preview)".

So when "Block unmanaged customizations (Preview)" is enabled, please allow the Owners and Admins with CRUD Permissions for Unmanaged Solution and its Objects.

This will be a supportive improvement related to another idea below

https://experience.dynamics.com/ideas/idea/?ideaid=144f18a9-9edc-ee11-a73e-002248504629