Just thinking it out for the first time, but I suppose from a rubrical perspective, a mask could be construed as an illicit vestment:
There is no provision for wearing a mask in the rubrics.
Moreover, how does the priest kiss the altar wearing a mask which blocks the kiss? Or receive Holy Comminion?
Clearly, a priest wearing a mask would disrupt, impede, and alter the liturgical action at the altar, forcing the priest to repeatedly remove, then reinstall, the mask.
So yes, a priest wearing a mask will have liturgical and moral implications.
And given the overblown hype of COVID19, and the non-effectiveness of the mask as PPE, I’m not sure an argument from necessity would be legitimate.