Ah wait, I think I misunderstood you.
I thought you meant the in-line create when choosing an entity from from a relation
This: Cannot create new related entity in form-views
But I think I misunderstood. You’re just talking about the general internal form view right? Yes, this has to do with creating entities using the internal form view. The core reason for this workaround is the lack of filtering of relation fields in internal form view.