I’m running in to the same thing. Very weird that Data Assets don’t seem to care about the “Private” and “Instance Editable” properties for BP variables. But I have to imagine there’s some way to have BP variables not appear, as it’s kind of crucial to what Instanced Properties and Data Assets are about.
It could just be a bug with the version of UE, as I’ve seen references to the fact that in my version of UE (UE5.1.1), there’s a bug where “Private” variables are still editable by subclasses. Maybe that bug also extends to this.