Lemmy comes in 2 parts the backend ( people will refer to this as the database and activitypub) and the front end lemmy-ui
The backend is the same as other instances and so data can be transferred, the Lemmy-ui is what you see. The differences in the UI package has no effect on the workings of the Database or activitypub.
From you POV it would be like saying How is your toilet working when you have a brick exterior and I have wood panelling. The outside of the house (lemmy-ui) doesn’t change how the toilet (database) works or how the water and waste is moved in and out of the house (activitypub).