There is, afaik, no explanation why there is more matter than anti matter, so maybe we just don't see it

Like, dark side of the universe or something ;⁠-⁠)

This is the baryon asymmetry problem, and indeed, one of the proposed solutions is an "anti-universe" that flows backwards in time. The theory goes that all the antimatter travelled backwards in time while matter travelled forward from the Big Bang, creating a mirror anti-universe. However, there has been experimental evidence against this theory, as antiparticles seem to move forward in time, just like their matter counterparts.

There are a bunch more theories on how matter dominated the universe, like electroweak baryogenesis and leptopgenesis! Those are a bit more complicated though and are difficult to explain in an internet comment.