Panasonic GH6 has a Micro Four Thirds lens mount and currently there are 132 native lenses available for this mount.
The latest released lenses that are compatible with the GH6 are the Brightin Star 60mm f2.8 II, the 7Artisans 50mm f1.2 APS-C and the Pergear 50mm F1.2 APS-C.
GH6 also has a sensor based image stabilization system that is up to 7.5-stops effective which means that all of these lenses will be stabilized when used on the GH6.
Since Panasonic GH6 has a Four Thirds sensor, it has a focal length multiplier of 2x so you have to multiply lenses original focal length with this multiplier to find the Full Frame equivalent focal length of the lens when mounted on GH6.
You may also also be interested in these:
Panasonic GH6 Lenses with Image Stabilization
Panasonic GH6 Lenses with Weather Sealings