Vias in 2D view have soldermask openings by default but they shouldn't. Vias should be covered by soldermask by default, and then users can override this in special cases when they want. It's a shorting risk to have them not covered with soldermask.
Interestingly, the gerber export doesn't include the soldermask openings on the vias (which is good, that's what we want) but that doesn't match what we show in 2D. So we should fix the 2D view to remove the soldermask openings for all vias (on top and bottom).
3D view matches gerber preview for ground fill vias but they don't match for trace vias because we're showing soldermask openings for all traces, which we should fix eventually but is separate.