As you say, it shouldn’t share a release group with the full album. I’ve seen the “Other” release group type used for these kinds of release groups, but the single type might do.
A relevant question is “Is this a release?”. This has been discussed before, see the topic “Clarifying “Release” in a streaming world” (including my personal stance). For reference, I’ll also link my old topic “Album tracks released as singles” from the old forums which seems to handle a similar issue.