Remote Play Hardware Decoding Broken since December 2021 Release

[gordan]

ISSUE
Remote Play with hardware decoding enabled no longer works on Linux clients since Steam client December 2021 release.

OS
Linux (CentOS 8), Nvidia GPU
Bug follows the Steam client version, not the GPU drivers or OS libraries, so definitely a Steam bug.

STEPS
1) Install Steam client, check for updates and apply them.
2) Go to Settings -> Remote Play -> Advanced Client Options
3) Tick "Enable hardware decoding"
4) Stream a game from a remote Windows machine running Steam

RESULTS
With hardware decoding enabled:
The streaming client exited unexpectedly (2)
With hardware decoding disabled, it works.

To prove pre-December 2021 versions of Steam client work with hardware decoding:
1) rm -rf ~/.local/Steam
2) restore ~/.local/Steam from a backup before the December 2021 release

3) Disable steam client updates by creating ~/.steam/steam.cfg with:
BootStrapperInhibitAll=enable
BootStrapperForceSelfUpdate=disable

4) Add this to /etc/hosts to positively prevent Steam from fetching its updates:
0.0.0.0 cdn.akamai.steamstatic.com cdn.cloudflare.steamstatic.com media.steampowered.com

5) Start Steam client.

6) Enable hardware decoding

Try streaming a game with hardware decoding. It'll work just fine.

EXPECTED
Hardware decoding should continue working as it has been for a long time.
There is very obviously a regression in December 2021 release that broke hardware decoding, and this is likely to cause a serious problem for people who are remote playing on Linux machine without much CPU to spare.

Edit: It looks like even without hardware decoding the Linux client after December 2021 still hangs when trying to remote play, intermittently. Restoring from an early December 2021 backup makes it reliably work every time, with or without hardware decoding, that version is rock solid.