i cant play in multiplayer and theres no one in the nexus and idk why

Multiplayer may work only with GOG Galaxy. I do not use Galaxy and have no menu option and multiplayer setting in NMS.

Translated with Google.

Do you have it enabled in the settings?

By default, multiplayer is turned on. You have a choice to play your own game, or join another. If you want to keep people out of your game, you have to turn off multiplayer in a sub menu.

So, chances are you didn't see anyone because there weren't any "near by" players who chose to join a game rather than start their own.

i know that but my save doesnt appear in multiplayer and i dont remember where do you turn off the multiplayer

You have to start Online first when it asks you about joining. If you start completely disconnected from the net it won`t even bring up the option. Then start game and go into your settings and LOOK to turn it off - It`s there. I can`t remeber exactly where but if I look I`m doing exactly what you should be doing. Just look and take your time.

You're always in a multiplayer game. You see the other players. And you can form groups. Regardless if you have chosen so start your own game. How much influence they have on your game, you can define in the setting.

Beside of the nexus there are not many encounters if you don't arrange a meeting. If you don't see anyone in the Nexus there are several possible causes: In the GoG-universe aren't this much players. And the multiplayer 'community' is small. Especially in some timezones. On the other hand it sometimes took some moments until I saw the others. In both cases: Did you spend some time in the nexus?

Maybe you have no network connection. Do you have connection with the online discovery service? Green (!) light?
If you don't have green light this could be an indicator that you are offline.