Hey Man, thanks so much! I was only able to figure out PVP, sadly. I did figure out how to make online bosses or single enemies but the hardest part was I had to re-code the networking for every single enemy. So if I had 12 enemies on screen, each one had to have it's own set of code which is terrible haha. I'm sure there's a way but I just never figured it out.
I still use Construct for some project but now I mostly use Godot. It has a pretty legit multiplayer system and you can credit your own servers with C++. (Which I've been studying for the past couple of months.)
I definitely recommend using Construct's multiplayer system. It has limitations, but it's an absolute blast to make multiplayer games to play with your friends. Best of luck to you!