My platform is Steam but this problem can occure on Xbox or Windows editions.
If it says offline but indeed you are online on the main menu Follow these steps : 🔽🔽 1- Try closing your firewall. If it didnt change anything make the next step. 2-Open your modem/router interface. If you don't know how, please contact with your ISP and get information how to do. 3-Click to the advanced. Then find Portforwarding/Virtual Servers menu. 4-Select HTTP for the service type then press scan, enter your IPv4 adress 5-Enter Astroneer port for the external ports. Be sure that you chose the correct protocol. (The ports which has got red box are the most reliable ones)   ‼️Note: All ports and portforwarding photos are at the bottom. Done! Have a Nice Day