So, the most annoying thing to do a mac build is to "sign" it (I don't remember the correct word for that, sorry).
You need a Mac computer and an expensive developer account. I don't have any of those.
But if you just push a unity build through Steam, Steam will sign it and it can be played on a Mac computer.
It does still comes with more bugs specific to the Mac version, and since we don't have a Mac we have to rely on our community to find those, but at least it's possible.