Caveat: its usually video game soundtrack items but can almost any track be basically looped in this way?
Probably helps that most music begins and ends on the tonic or maybe they slice the track in half and cross-fade or something?
How can it be (easily) replicated
This is a core capability for anyone who calls themselves a video editor, and all video editing software can support this easily.
Ok, im not tho and I’m more interested in the how than the bona fides
That’s was all to say that just any video editing software will get you there. Pick one and try cutting where it makes sense. Look up how to crossfade in the software you choose.