The positions at which the most obvious wobbles occur seem consistent, making me think this issue is due to the screen? Could these be the result of deviations in the plane of the screen due to something structural behind it? I made a Krita (drawing software) canvas cover most of the screen, then tried to draw straight diagonal lines.
My Dell XPS 13 2-in-1, using the active stylus that came with it, draws wobbly lines.