Satisfactory is a first-person open-world factory building sim from Coffee Stain Studios and while it works well on Linux with Steam Play Proton the online networking had a big issue.
For people with multiple network connections, trying to join others online would be problematic and most of the time just not work at all with an error message. There were workarounds like disabling other connections but it obviously wasn't ideal and just another barrier. Thankfully the Proton Experimental release from October 13 notes a single change as "Fix connection issues in Satisfactory on systems with multiple network interfaces".
I came across the issue personally too when trying to join a friend online, which needed me to fully disable a Docker networking interface I had setup at some point in time. It was definitely frustrating.
Thanks to that fix you can now join up easily with friends online in Satisfactory when played on Linux with Proton.