The base game doesnt have any official multiplayer, and cdpr scrapped their original plans for a gta online-style mode after launch. You can try the cybermp mod if youre interested in unofficial multiplayer, it supports up to 20 players for racing and deathmatches though its still in development.

The phantom liberty expansion and 2.0 update came and went without adding multiplayer, which pretty much closes the book on that for the current game. Something interesting though, there are job listings suggesting multiplayer features might show up in project orion, the upcoming sequel thats in early development.

For now, your only real option is that cybermp mod if you want to explore night city with friends, but keep in mind its not officially supported and doesnt include quest content yet.