hey, not really, the thing with multiplayer is that, you dont need much code or customization work
well depends on which multiplayer sdk you are using, i have only used photon and it is good for beginners, all multiplayer sdk do it help you to connect others together and relay messages across the servers , so a single player game can be a multiplayer game, you dont need to add any special configuration or customization, depending on what kind of multiplayer game you are working on, and you will need to find a multiplayer sdk that fit what you are looking for a build of it and also check their docs. so that project in the demo can be like that and all you have to do is that any player that join the lobby will have a character like that and the movement and the address on their head e.t.c