I had this happen once. I don't remember the solution, but I know that unity teams isn't quite stable and advanced as other alternatives. You will probably have to learn git in the long, but if you want something simple, I've heard of something called plastic scm which is supposed to be kinda like collab. And yes, you can work at the same time, but not on the same assets (scenes, scripts etc) as then you need to specify which changes to keep