BigPicture: doesn't focus the right game window in case the first opened window is not the game itself

[ranplayer]

Your system information

• Steam client version (build number or date): 1676336721
• Distribution (e.g. Ubuntu): Arch Linux
• Opted into Steam client beta?: [Yes/No] No
• Have you checked for system updates?: [Yes/No] Yes

Please describe your issue in as much detail as possible:

New/old BigPicture doesn't focus the right game window in case the first opened window is not the game itself. The games I've noticed this issue so far:

• Injustice 2 (Steam Id: 627270)
• Guilty Gear XRD Rev 2 (Steam Id: 520440)

(the first release of the new BigPicture didn't have this issue)

Specs:

• GPU: RX 6700 XT (Mesa 22.3.5)
• Desktop Environment: KDE 5.27

Steps for reproducing this issue:

1. Launch the game with the new or old big picture
2. Check that the game will be kept in second plan (you bring it to first plan with Alt + Tab or Guide Button + Start)

[ranplayer]

New game affected by this: Singularity (SteamId: 42670)

[ranplayer]

I've found out a current workaround for this issue using KDE Plasma 5.27:

• Set "Big Picture mode" to run in a window instead of fullscreen
• By default it won't start maximized for some reason, so it's necessary modify the window settings and apply some rules (maximized horizontally and vertically + no title bar and frame)

(even though some of these games still need a mouse click to gain focus)