Disabling Steam notifications while in-game doesn't work

[Lastique]

Your system information

• Steam client version (build number or date): 1705108172
• Distribution (e.g. Ubuntu): Kubuntu 22.04
• Opted into Steam client beta?: No
• Have you checked for system updates?: Yes
• GPU: RTX 2080Ti

Please describe your issue in as much detail as possible:

Setting "Show Notification Toasts" to "When I'm not in-game" has no effect, the notifications (e.g. about achievements) are still shown in-game.

The notifications cause severe performance issues, the frame rate drops to like single digits while the notification is displayed. Which is why I disabled the notifications in settings.

Steps for reproducing this issue:

1. In Steam settings, Notifications tab, set "Show Notification Toasts" to "When I'm not in-game".
2. Run a game (in my case, Thief, app id 239160) and gain an achievement.

[Lastique]

The notifications cause severe performance issues, the frame rate drops to like single digits while the notification is displayed.

This can be mitigated to some degree by disabling GPU accelerated rendering in web views in Steam settings. When a notification appears or disappears in-game, there is still severe stuttering, but at least the frame rate remains playable while the notification is shown. Of course, disabling GPU acceleration makes Steam UI very sluggish.

@kisak-valve When will this be fixed?