Definitely 3D. The physics is all there, you have light paths that bounce off the mirror going to all the depths behind it, and the best evidence is that your two eyes will get slightly different images to each other.
“Resolution” is an odd term in this context. I suspect the technical term for a mirror is ‘grain’ and it would correspond to the size of the molecules of reflective material used.
Assuming it’s a ‘normal’ household mirror this reflective material is on the back side of a sheet of glass, and there are some other aspects to consider such as the clarity and flatness of the glass.
If the mirror is a “first surface” mirror and the light does not go through glass, but instead reflects right off the front surface of the mirror, then you’re in serious optical instruments territory.
The most perfect ‘mirror’ I ever had/saw/used is a silicon wafer that was rejected for making semiconductors because it was not quite flat enough. These wafers have to be flat within a few molecules. The reflection is eerie because it is so perfect and there is no distortion from going twice through a glass layer.