In addition https://www.youtube.com/watch?v=DydIhwLrbMk which tries to make portals act “real” by treating them as spacetime with an unusual (but not mathematically disallowed) geometry.

Yes, they are fictional, so they behave however Valve (and fan works) want them to behave, but trying to bridge the gap between fictions and current physics models and be a fun and enlightening experience.