Player's vision

Is there a way to put up invisible walls so the players can’t see through them?

That is what Dynamic Lighting is for. I would suggest reading through the documentation and playing the two tutorial games on Astral to learn more about it.

Yes I did, but when you create a bridge or walkway the players can see rooms to the side even if though they shouldn’t

Draw DL walls along the sides of the bridge to create walls. It will also stop them from walking off the bridge.