Main Steam window disappearing when trying to install a demo via a news item (library mode)

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Your system information

• Steam client version (build number or date): 1771028631
• Distribution (e.g. Ubuntu): Devuan excalibur
• Opted into Steam client beta?: Yes
• Have you checked for system updates?: Yes
• Steam Logs: excerpted via tail -f ~/Steam/logs/*(.) in zsh
• GPU: RX 6600 XT

Please describe your issue in as much detail as possible:

The main Steam window mysteriously disappears and remains gone (presumably deleted). It is not possible to re-open it via the menu attached to Steam's icon in the system tray; however, Steam can be shut down normally via that menu.

I note that the log contains some X BadWindow errors, which suggest that the window is deleted but Steam thinks that it isn't.

Steps for reproducing this issue:

1. Find and open a demo news item in the “What's New” section in the main window or via the library page for a related game.
2. Scroll down it a bit if needed so that you can see the “install demo” button.
3. Click on that button (specifically that; don't go to the store page!) and watch the Steam window vanish.

100% reproducible.

I used the demo for “Vampire Crawlers” linked from a news item posted for “Vampire Survivors”. I do not see other demo news which I can use for testing at this time.

Doing the install via the store page works without problem. It appears to be required that that the news item is displayed in library mode rather than as part of a web page to be able to trigger this bug.