Hello @Toren-T, besides Warframe, what other games have you seen this behavior with?
So far I have tested Warframe(from the log) and Forza Horizon 4.
With a bit more testing Risk of Rain 2 I can see multiplayer servers, The Binding of Isaac: Rebirth Daily leader boards work, and TrackMania2 Stadium I can see multiplayer servers.
Thanks @Toren-T, since the issue isn't an unconditional failure, I think it would be better to evaluate this feedback on a per-game basis, and we're using one issue per unofficially supported game title. I've gone ahead and transferred this issue report to https://github.com/ValveSoftware/Proton/issues/167#issuecomment-885811626. Feel free to also add a note to #4667 for Forza Horizon 4.
Compatibility Report
System Information
I confirm:
steam-230410.log
Note: This is one of the smaller logs I got due to the app crashing immediately without an internet connection.
Symptoms
Any program I run using the Proton Experimental build lacks a internet connection. All other versions of Proton I have used have had internet access.
This issue persists regardless of network drivers. I have tested using systemd-networkd with systemd-resolved and NetworkManager with systemd-resolved, openresolv and dnsmasq.