Does a MacMini M2 Pro support Qty 3, 4K monitors running at 60hz each?

Yes the Mac mini M2 Pro can do that.

see the M2 Pro section at > Connect a display to Mac mini - Apple Support

and the M2 "Display Support" spec's at > Mac mini - Technical Specifications - Apple

No the M2 Mac mini non-Pro version only supports 2 displays.

The 14" and 16" M2 Pro MacBook Pro models support 2 external displays.

The 14' and 16" M2 Max MacBook Pro models support up to 4 external displays.

see > MacBook Pro 14- and 16-inch - Tech Specs - Apple

and > Use an external display with your MacBook Pro - Apple Support