Styling Geo Primitives

Use GeoStyling:

GeoGraphics[{GeoStyling[Red], GeoDisk[{60, 20}]}]

GeoGraphics uses a predefined opacity for GeoDisk primitives. Calling Opacity prior to the generation of the GeoDisk object will not change its value.

A possibility is to modify the opacity once the graphics is created:

graphics = GeoGraphics[{Red, GeoDisk[{60, 20}]}, GeoBackground -> None];

graphics /. Directive[Opacity[0.2`]] -> Directive[Opacity[1]]