I figured it out, see this thread over at the Arch Linux forum.
TL;DR;
When using systemd-networkd and systemd-resolved I had to install lib32-systemd for the Steam client to work. Still no network in Proton 5.13.
When I changed to dhcpcd, the network worked in both the Steam Client and Proton 5.13.
This issue can be closed.
This looks exactly like my issue on Ubuntu. However installing libsystemd0:i386 did not solve it. What did you do afterwards exactly... ?
I switched to dhcpcd instead. Fixed the network issues with Steam and proton.
I solved my issue now, by installing nscd!
And yeah, I had the exact same thing with Steam and proton.
I have no idea why it helped, all getent hosts results look the same etc...
System information
Please describe your issue in as much detail as possible:
It all started when I was trying some games through Proton (Killing Floor 2 and GTA V), but I think the real problem is the Steam Client Runtime. Both games seemed to "start", but none of them had a network connection. Perhaps same issue as this where someone suggests that libgnutls fails to load which results in failed network attempts.
I searched around and someone suggested to use steam runtime instead of steam native which I was using, but same problem, still no network in Proton games.
Since I have the games on a separate drive I figured I might as well try a fresh install of Steam. So I deleted
~/.local/share/Steamand~/.steam. Uninstalledsteam-native-runtimeand all of the dependencies that came along.Now when I run the client it only shows a modal "Steam - Fatal Error": "Fatal Error: Steam needs to be online to update. Please confirm your network connection and try again."

Since Steam (runtime) worked when I had the
steam-native-runtimeinstalled, I assume some of its dependencies perhaps are required and should be bundled with the runtime? But I can't figure out which one. I'm guessing that if I get Steam Runtime to work, then perhaps the networking in Proton games will start working too.List of my installed multilib packages
Steps for reproducing this issue
steam-native-runtime~/.local/share/Steamand~/.steamsteamWhat I've tried
So basically I've been trying to figure out if there is any
sofile missing.Running
steamand trying to figure out if something obvious is missing. No luck.See output
crash_20201229105626_5.dmp.zip
Find missing runtime libraries
(As suggested in the Arch Wiki.)
Running
env DEBUGGER=gdb steam, then typingrunSince I have no idea how to use gdb that didn't give anything new.
See output
I've tried the
-tcpswitch (#7232)Same error; still no network.
Installing
steam-native-runtimeNetworking in the client and native game now works but networking in Proton doesn't.
Gist with my System Information