The 2019 input system package provides a component called Player Input Manager. It has the option Join Player When Join Action Is Triggered" as Join Behaviour. How Can I trigger that action? I can't find anythink via search engines and I'm a newby to unity.
Further explanation: I would like to have a main menu where every player can press a button to join the game. Then the game shall start and the players shall spawn at different predefined positions. I am happy with links to tutorials, too.
Maybe I'm late and you have already found an answer, but I may still be helping some other people in the future. I don't have anything experience with this Join on Trigger (yet) too, but I think I get what is going on. When you select the option, you get a little menu beneath it. Then you can add an action and if you click on the '+' symbol, it give you a couple of options. I assume for your situation 'Add binding' will be the best option. Click it and then a binding will be added. When you then double click on the binding, you can choose a path. Define your path and if you dont want to look for the path yourself, you can click on the 'listen' button and then press a key.
I don't know how much your knowledge is of the new input system, combined with local multiplayer, so here is a link to a video that will go over the basics: https://www.youtube.com/watch?v=D8nUI88POU8&t=300s
