This is a limitation of the electronic shutter used in your camera. Actually, it is a limitation of nearly all electronic shutters, some brands cap it at just 1/60s, some more, such as Panasonic with a 1s cap. It probably depends on the generation and these things are relatively new and bound to improve in future digital cameras.

A mechanical shutter is a simply mechanical device. It moves across the sensor rapidly and is bound to make some noise. Since the GX85/GX80 is a Micro Four-Thirds mirrorless, the sensor is smaller than that of DSLRs so is the shutter, so it makes less noise. Still, there is nothing that can be done to change the amount of noise produces. On a DSLR there is a mirror which makes more noise and it can be slowed down or dampened which is what Quiet mode does for Nikon DSLRs but that does not change the shutter noise either.

Some cameras have such quiet shutters that they emit an artificial noise to sound more like it is taking a photo. That can almost always be turned off but shutting off sounds in a Settings menu. Check if you do not have one such sound enabled, since you camera should be comparatively quiet.