Just curious, is it possible to make a proper rotation without tweaking after?
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You need to shear the vertices / edge loops.
Select the edges/vertices in edit mode.
Press CtrlShiftAltS to go into the shear operation.
During the operation you can press X or Y to constrain it to the respective axes. In my example I enter the number -1:
CtrlShiftAltS, Y, 1, -
After that simply extrude in the X direction then scale it to zero along the x axis.