For example, these two releases belong to different release groups:
They have parallel tracklists where each track is a different “mix” - one has the vocal track, and the other does not. For example, https://funkydl.bandcamp.com/track/pieces-of-a-thesis-instrumental is the karaoke version of https://funkydl.bandcamp.com/track/pieces-of-a-thesis-ft-abioseh because the vocal track was muted/silenced/deleted/removed.
I think these two release groups are sufficiently related that they should be linked with a relationship. Is https://musicbrainz.org/relationship/04e0449b-6fb0-48f6-8b9d-0bd41d9b8d76 appropriate, or is the appropriate relationship type missing?