[AC Question]

My Bluetooth mouse only works properly in portrait mode, i.e., when rotating Smartphone to landscape display, mouse control remains in portrait mode.

[Rukbat]

Think about it. Turn a desktop monitor on its side. How would you get the mouse to "orient properly"? You wouldn't - neither device (the desktop or the phone) is designed to have the mouse orient so that pushing it toward the front of the mouse goes up the screen when the screen is turned.

About all hou can do is turn the mouse sideways and use it that way.