Both me and my wife are playing on PC, 2023, 1.2.2 version, and have the same issue when it comes to building in multiplayer. As described in posts above. Im hosting and can build, place etc, and i see the stuff she builds, but for her, she can only see the blueprints(even though she places the material and it gets buildt). When i relocate it, it appears for her. When she logs out and in again, its "fixed", but only the pieces she has placed and buildt. When she places a new wall, same problem again.
Have also tried shared world etc, but the problem with building consists.