since the hardware that i run my Ubuntu mate on isn't that common, being a 2-in-1 lenovo laptop , i was unable to find anyone with a similar problem to mine. that is the rotation of the screen is sideways as if the system recognizes my laptop as a tablet.
this problem stops after logging in, because i changed the settings of the screen to the appropriate alignment
a picture to clarify
Open the Displays control panel and tick the box that says Show monitors in panel.
You can now use this monitor applet, the one that look like a monitor with a set square over it below, to flip the orientation of the attached display(s).
I did that before; it worked for the desktop but not the booting nor the login menu
I know this topic is old, but for the ones who still wonders for the rotation of the booting and login menu. You can do this : open Displays control panel and once you are done click on Apply system-wide, or aplly for all users. It worked for me.
