To ensure that each Backstage component has an owner and that owner is a Group (rather than an individual User) that is present in the catalog, create a check with the following attributes:

Field Input
Name Ensure owners are present on Backstage entities.
Description Declaring an owner helps others understand who is responsible for this Component. Owners should be groups, rather than individual users.
Data source Entity Metadata (this is built-in).
Fact Has Group Owner
Fact operator Is True