Max Shutter speed
Panasonic GH5S can shoot continuously at max speed of
12.0 fps and has max shutter speed of
1/8000 sec. GH5S also has an electronic shutter which can shoot silently at max speed of
1/16000s. One thing to keep in mind is that electronic shutter may cause rolling shutter / jello effects, and also banding issues under artificial light on your images.
Flash
Unfortunately GH5S doesn't have a built-in flash but it has a flash shoe for mounting external flashes.
Focusing
Panasonic GH5S features a Contrast Detection autofocusing system. The AF system has 225 points to choose from. Panasonic GH5S also features
Face detection AF where it intelligently detects the faces in the frame and locks the focus automatically.
Focus Stacking
Macro shooters will love Panasonic GH5S's Focus Stacking feature. In this mode, GH5S automatically composites multiple shots taken at different focal positions using focus bracketing to create a single image with maximum depth of field.
Post Focus
Panasonic GH5S has a special Post Focus mode which uses its 4K video and focus bracketing features together to shoot and stack a burst of images into a single image which you can change the focus point on the LCD screen after it is taken.