If it helps, randomly and sparsely (with no apparent rule as for when/when not, and little frequently), I use
d to get that behaviour (that I'll call the "taskbar flashing app protocol": instead of launching directly in a new window as any new app, it goes to the taskbar and the icon flashes) when running anything (maybe there's a rule that I haven't managed to catch), specially things that require an UAC prompt but not way all of them, randomly and sparsely instead. I have 4 computers with Windows 7, 10 and 11, I think I've got this behaviour some few times in every (I insist, randomly and sparsely in my case).
I use the past because I don't recall having it recently, maybe like 2-3 months.
Idk if this behaviour (the "taskbar flashing app protocol") is expected behaviour in some situations (like -fictional- "the new windows manager is busy or overflowed and it does it to not lose the app run or to avoid doing half-app runs", or -fictional again- for security reasons), or if it's a bug.
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I've researched this a bit
launched app goes to taskbar as flashing icon - Google Search .
My best finding is likely this
Windows 10 Taskbar program flashing but not opening when called - Super User , Windows 10, the OP's trying to open another file from Explorer for an already open app and gets the flashing instead. From the replies it seems to be expected behaviour in this case. I'd suggest seeing if Photos is already open somehow, maybe with a never closed pic?
More theoretical or for specialists
c# - application causing orange flashing in taskbar - Stack Overflow . The OP says:
"I think we will end up advising to set registry key HKCU\Control Panel\Desktop\ForegroundLockTimout = 0. It is not ideal, but it seems to be the only thing to fix the problem." Imo, don't do this w/o at least researching about that key. Also, this is a 2011 thread about Windows 7.
This thread
https://www.reddit.com/r/Windows11/c...ng_on_taskbar/ is about Windows 11 and a complicated maneuver that I don't understand well. The OP is suggested
"It is possible to turn the app flashing up all up (it's an option in taskbar settings), but not specifically on startup to my knowledge" (I've gone to my taskbar settings in my W10 and I haven't seen anything that could be this cryptic option to my understanding, maybe it's for just W11) and the OP replies
"Thank you so much, this fixed it. After booting up my pc today all those pre-opened tabs no longer flaunting me to click on them."