Which market?

And which IP? Local?

The vast majority of people will not even be able to enter an IP adress to connect to each other, even if they wanted to. You need port forwarding for that and find out your external IP adress to even start. That can be dealt with of course, but this is deprecated for just about any application. Some olden games that need such things can be played over special software that basically emulates a local network with vpn techniques.

Ask people nowadays to enter IP adresses and they will think you are trying to "hack" them.

Because of the router firewall, you need some kind of brokering. Itch does not have this. Steam has, and they are the market. So to answer your question: it is nonexistent in a commercial market. A game will just use the tools of the game platform to broker a multiplayer match, or have it's own server.

Maybe some enthusiast will give insights to this, but I doubt that there is a nieche group that likes games because of that, as there is for pixel art or text games. It is just not done anymore for lots of technical reasons to enter IP adresses to play a game together.