I didn't realize there was a different driver for ubuntu. AMD's site directed me to this version and the 20.10 version earlier this year when I got the card.
Would just uninstalling the AMD driver suffice to revert to mesa?

Uninstalled AMD drivers, installed Mesa drivers fresh. Re-installed steam
Same issue
https://gist.github.com/s1ugh34d/e606f5e5be1a3e285e1fa09b3f01581c

Same X errors

I believe I've had more or less the same problem for months now but I am using an Nvidia graphics card. The native client stopped working the same way multiple times after installing updates for either Ubuntu or Steam. The flatpak version used to work for me but that one also stopped working eventually.

Part of the error message is simply Could not connect to Steam network.

Steam error log:
https://gist.github.com/SteffenL/ccf72b1b6f31373743b4e77ccf98c234

I do not know if this is useful:

$ sudo lshw -c video
  *-display                 
       description: VGA compatible controller
       product: Ellesmere [Radeon RX 470/480/570/570X/580/580X/590]
       vendor: Advanced Micro Devices, Inc. [AMD/ATI]
       physical id: 0
       bus info: pci@0000:02:00.0
       version: ef
       width: 64 bits
       clock: 33MHz
       capabilities: pm pciexpress msi vga_controller cap_list rom
       configuration: driver=vfio-pci latency=0
       resources: irq:11 memory:c0000000-cfffffff memory:d0000000-d01fffff ioport:d000(size=256) memory:fb800000-fb83ffff memory:fb840000-fb85ffff
  *-display
       description: VGA compatible controller
       product: GP102 [GeForce GTX 1080 Ti]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: irq:68 memory:fa000000-faffffff memory:a0000000-afffffff memory:b0000000-b1ffffff ioport:e000(size=128) memory:c0000-dffff

For your information, physically removing the AMD card does not solve my problem.

Update

I no longer have a problem with Steam on Linux. It turns out that maybe my IP address was on some blacklists. After changing my IP address, I no longer have issues with Steam.

I had a similar issue today after updating the Steam client on my Ubuntu 20.10 machine, and it seems it cannot be launched when docker-compose is running (I'm developper, it's my dev stack). @SteffenL : you give me an hint about IP issues, and docker/docker-compose create local virtual networks and so, IPs. Thank you :wink:

I might have had Docker and Compose installed but it seemed more likely that connections from my IP address were blocked somewhere along the path to the Steam servers when using the client for Linux. I didn't have the problem while using Windows, and I didn't have the problem when connecting to Steam through VPN on Linux, only when I was using my real IP and Linux at the same time. I also had connection problems on a handful of other websites. The problem persisted only until I was assigned a different IP address from my ISP.