The shortcut to rotate clockwise is Numpad 6, counter-clockwise is Numpad 4. Then you rotate the view around the selected object's origin or ther median point when multiple objects are selected.
However, if you have Blender at default settings, it can be that it automatically switches to Perspective. To switch back to Orthographic you can press Numpad 5.
If you don't want Blender to switch automatically between the perspective and orthographic views, you can disable it in the Preferences under Navigation > Orbit & Pan > Auto.
But note: when you disable it, it also does not switch to perspective view when for example you are in orthographic top down view and start rotating the view by dragging the MMB. And if you are in perspective view, it does not automatically switch back to orthographic if you e.g. press Numpad 7 for top down view.