Opened windows don't have focus on Windows 10

I can't duplicate your problem, so this must be some startup product that is stealing the focus.

It will be easier to use Window Focus Logger. Using the GUI version WindowFocusLoggerGUI.exe worked better for me than the batch version.

For turning startup items off and on again, a better tool is autoruns.

If you Right Click (not Hover) in Windows 10 2004, you should see a sub-Window offering various things to do, but not open the application. See the screen shot below.

Left click allows you to open the app.

I am thinking this may have been a modest change as Windows 10 evolved. Only very occasionally (once or twice in a week or two) would the icon flash. If this is your case, you can probably ignore it.

If this is happening all the time, use the following steps:

(1) Open cmd.exe with Run as Administrator and run:

(a) dism.exe /online /cleanup-image /restorehealth

(b) SFC /SCANNOW

Restart and test.

(2) If DISM / System File Checker do not fix this, run a Windows 10 Repair Install from the Microsoft Media Creation Link.

https://www.microsoft.com/en-us/software-download/windows10 Download the Windows 10 ISO to a USB Key and run Setup.exe on that key.

(3) If something has gone very wrong, you may need to back up Windows and Reinstall. In a good Windows 10 system, right and left click work properly. Make sure when doing this that all drivers (and BIOS) are up to date.

Addendum: I have also watched my own system and read articles on how Microsoft is changing things. So make sure this is not just one of the ongoing changes you are seeing.