The Gizmo manipulator should not “snap” if you’re not holding down the constrain modifier key (Shift). This would either be an issue with the input device being used, or possibly a gimbal-lock situation which can occur if the rotation axis lines up perpendicular to the screen plane. This can result in abrupt transitions. If rotating around an axis in this situation make sure you are dragging in a circular motion around the outside of the manipulator, and not dragging through the manipulator at any point. The farther away from the center of the manipulator you drag, the slower and more controlled the rotation will be. Changing the camera angle may help.
Please also note that especially dense meshes or tools with many millions of points visible on the screen at one time will perform more slowly with all aspects of navigation. So rotating such a mesh will also perform more slowly and may lag a bit or undergo abrupt transitions and appear to be “snapping”. Dropping to a lower level of subdivision if it is available would improve this performance.
Custom Gizmo Snap angles can be defined in Plugins> Misc.
Precision camera rotation can be achieved with the Transform> Axis Rotation feature.
