MSFS loses focus

I7 6700 cpu, 32gig ram, gtx 1660 super 6gig, 500 gig SSD, Windows 10.
MSFS asks for a new NVIDIA driver (older version than what is installed). Runs great no stutter, 34 fps.

One problem. When a new window appears, it loses focus. No mouse response. No other open windows.

I have to to the task bar, minimize the window and select it again on the task bar. Becomes active again.

Anyone have a clue? Thanks.

If I inadvertantly swap to a new window in Windows I loose the mouse. I need to change the active window back to MSFS and then the mouse is active. If you have an app that opens a new window while MSFS is running, that would cause the loss of focus.