Nobody can tell you anything without exact system and version information.
I don't think you can do anything to prevent Photoshop "stealing" the window focus whilst starting up. It does that here on Windows 10 - I just start Photoshop at a convenient time and leave it running in the background.
It's a known issue, which will hopefully be addressed in the next update.
What you could do as a (very) clunky workaround until then, is to minimise Photoshop before exiting to a part screen state like below. It will remember that when next started, so it will be easy to click on the full screen window behind it. When fully open, hit the maximise icon. It's rough and dirty, but the best I can think of.
- Adobe Photoshop CC 2017
- Windows 10 Home 64-bit
- Intel Celeron N2840 @ 2.16GHz
- 4.00GB DDR3 @ 666MHz
- Acer Aspire ES1-512
- Generic PnP Monitor (1366x768@60Hz)
- Intel HD Graphics
"minimise Photoshop before exiting to a part screen state like below. It will remember that when next started"
Thanks for this suggestion, Trevor. As the program cannot be minimized while starting up, yours seems like the best suggestion for the time being. I'll put it to use when I'm done working today, and let you know how it went.
Also, good to know the problem is known about and that they're working to resolve it. This morning, PS covered my other windows no less than 9 times before it completed opening. I think your suggestion will make a difference until such time as Adobe fixes the problem.