There are new Network options that can fix that. Having someone join your game is no longer possible out of randomness, they have to have you as a friend, or you have to be in the Space Anomaly or (Nexus) to join.
The only way they would know is if you keep building repeatedly without needing to mine. I've played Beyond for 60 hours, and nobody has ever joined my game as a group mate, and even teleporting to their base via the Interstellar Portal makes them invisible it seems.
So Tld: The game is always Offline.
If you didn't forget to run the trainer as an administrator and you're playing the same Steam version, then you're welcome to use the File Update Request situated on top of this page, where a monkey will verify and transfer your demand as soon as there is two(2) more people filling a report.
Thank you for understanding 🙂