I see the same on guixsd with amdgpu. Small mode works but regular mode doesn't. Friends, messages, downloads and the store do not work as pictured in the OP.
Same on Gentoo Linux, nvidia+intel (optimus).
Hello @YellowOnion, your issue is already being tracked at https://github.com/ValveSoftware/steam-runtime/issues/462 and that is most likely a distro-specific issue.
Hello @namtsui, @pclouds, while the high level symptom of steamwebhelper failing to start may be the same, the cause can be completely different. I doubt that you're seeing the same issue as @YellowOnion. Your issues should be evaluated separately. Blind guess that @pclouds is seeing https://github.com/ValveSoftware/steam-runtime/issues/458.
Closing as a duplicate of https://github.com/ValveSoftware/steam-runtime/issues/462.
Thanks @kisak-valve you guessed right. Installing zenity worked.
Your system information
Steam client version (build number or date):

Distribution (e.g. Ubuntu): NixOS 21.05
Opted into Steam client beta?: No
Have you checked for system updates?: No
Please describe your issue in as much detail as possible:
cef_log.txtisn't created,cef_log.previous.txtis dated before the update.