You can go to the Item and modify the “default list widget” and set the visibility to false. Then it will not show up in the automatically generated cards in the overview page. See OH 3 Tips and Tricks for a way to rapidly do this through the REST API for a lot of similar Items.
Alternatively, if it’s not something that needs to be surfaced, you can exclude if from the model entirely. Nothing says you have to include everything in the model.
What cannot be done is to have one Item be a member of more than one semantically tagged Group. So you can’t put them all in the closet and then also put a few in another room.
I think we’ll need more context. I’ve not encountered that before but with more context I might be able to hazard a guess.