Looked into this a bit more and the articles showcasing the features were actually all based on pre release insider builds. Turns out these features didnt make it to 21H2 and Windows 11 got released, and Microsoft seemingly decided to make them excusive to that. Curious if they still exist on Windows 10 insider builds.
As to this mystery, it remains, as I have never seen a feature update that is no more than a few megabytes in size and just installs like a small windows update patch. The cumulative update I was going to try out to see if it broke, vanished so the system is left in its current state.
Maybe 21H2 is only a tiny update over 21H1 but could never really get info on it other than you are supposed to have 20 gigs of space free before doing the update.