It would be nice if different polygroups didn’t remesh together, or if there was an option to allow for this behavior. This is useful for symmetrical objects that touch along the center-line of the scene.
Voxel Remesh / Boolean union & QuadRemesh all keep the facegroups.
You will lose the facegroups when you turn off facegroups when you’re QuadRemeshing, but keep it selected and you should be fine - at least in version 1.91 beta. Maybe wasn’t a thing in version 1.90