Steam Play's "supported titles" no longer supported?

[michaelneverwins]

Your system information

• Steam client version (build number or date): Sep 17 2021, at 04:30:38
• Distribution (e.g. Ubuntu): Linux Mint 20.2
• Opted into Steam client beta?: No*
• Have you checked for system updates?: Yes

* I first noticed this issue while I had Steam Beta Update enabled, but I disabled it to see if it would make a difference, and I'm seeing the same thing now that it's disabled.

Please describe your issue in as much detail as possible:

I recently noticed that the games which I had known to be officially supported by Steam Play — which had previously appeared in my library with the note "Proton [some version] selected by Valve testing" — now have "Proton 6.3-6 selected by you for this title" (6.3-6 being the Proton version I've selected in my global Steam Play settings under the "Enable Steam Play for all other titles" checkbox). Additionally, it seems that I no longer have the ability to install these games when Steam Play is enabled only for supported titles.

One example is Downwell (which, if I'm not mistaken, used to run with Proton 3.16-9 by default as selected by Valve testing). In my compatibility settings for this game, the "Force the use of a specific Steam Play compatibility tool" box is not checked. If I uninstall Downwell, go into my global Steam Play settings, uncheck "Enable Steam Play for all other titles" (leaving only "Enable Steam Play for supported titles" checked), and restart Steam, then the option to install Downwell is unavailable. This seems to be the case for all of the games which I had known to be officially supported.

Although this isn't a major problem for me (as I usually keep the "Enable Steam Play for all other titles" box checked), having the supported games run with the verified Proton version by default was convenient. I'm curious as to whether this official Steam Play support now applies only to SteamOS or some subset of Linux distributions.

Steps for reproducing this issue:

If Steam Play is enabled for all titles:

1. Open the Steam library.
2. Select a game which is:
   1. officially supported by Steam Play;
   2. not currently forced to use a specific Steam Play compatibility tool.
3. Click the "Show more details" button to see if the expanded details section indicates that a Proton version was "selected by Valve testing".

If Steam Play is enabled only for supported titles:

1. Open the Steam library.
2. Select a game which is:
   1. officially supported by Steam Play;
   2. not currently installed.
3. Check if the game can be installed.