Problem/Motivation
Content Moderation adds two options to Workflow states; "Published" and "Default revision". Default revisions are ok for all entity types that use Content Moderation because we currently require revisions, however not all revisionable entity types (even in core) are publishable.
(The publish we are talking about here is related to the 'status' field, not a workflow state called 'Published'.)
See also:
#2830581: Fix ContentModeration workflow type to calculate correct dependencies
#2850627: Do not require a revisionable entity type when using content_moderation.
#2825973: Introduce a EditorialContentEntityBase class for revisionable and publishable entity types
#2812811: Use EntityPublishedInterface during moderation of entities to add support beyond nodes
#2850353: Test content_moderation with a non-bundleable content entity
#2842692: Warn users before enabling moderation on an entity type that can't be (un)published
Proposed resolution
Show a warning in the entity type selection modal in the workflows settings, if an entity type isn't publishable.