For what it’s worth , it works in Maya. I have tested this many times in he past. It is a Blender thing. I am not sure if there is a setting to change. But what I have done in the past is just make a special object only for baking.
Seems to be a recurring theme lately. But remember you don’t have to keep the same mesh through the whole process. I rarely do. Think outside of the box.
It is not uncommon to have 3 versions of the same mesh during the baking process.
Just take AO maps for instance. Some parts are animated so they can’t cast a shadow, but need to receive shadows. Some small parts are duplicated and cause multiple shadows. But only one if them is used in the map so only one if them gets baked. Yet multiple duplicates of that part are used to cast shadows on other parts.
Maybe the whole thing is animated, so it has to be exploded and then baked. Maybe the mesh needs to be separated do you can paint it cleanly on all sides. Maybe parts are too close or touching and you get normal map errors.
There are all kinds of scenarios.