If it’s a Cubase problem ONLY why do very few other Cubase users complain about this?
It does seem that in most posts like this that the user answer is usually “It doesbn’t happen using X or Y software” etc. This makes me think that a Windows setting made for the other software may be something that disagrees with the settings needed for Cubase to work.
However, anyone with a solution would really need a lot more detail in the post to make an attempt at fixing this particular problem.
I mean, how do we know that there might be jitter in the Pro Tools if it had been installed after Cubase rather than vice versa? Many unknown variables.