There was another thread where someone was asking something similar. Here’s the thread. New construction and demolition without geometry intersections - #5 by arcus
Speaking for myself, in order to prevent these interactions I slice off the parts we are going to demo and then explode, group, and change the layer to a demo layer which is generally turned off.
I typically have 3 separate models: an existing, demo, and proposed model. The existing is more or less a backup, and the proposed is the active BIM file. I split/explode/group/changelayer the demo elements in the BIM model during the design process and once I know exactly what is being demo’d, I create a separate demo file (from the existing model) with that demo geometry included and nothing new. It makes it easier to document.
You could technically leave the demo’d objects in the primary BIM file, but then you would have to turn off all the new stuff in your demo plans. It’s much easier to just make it a separate model.