Max Shutter speed
Sony RX100 IV can shoot continuously at max speed of
16.0 fps and has max shutter speed of
1/2000 sec. RX100 IV also has an electronic shutter which can shoot silently at max speed of
1/32000s. 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 RX100 IV doesn't have an external flash shoe so you are limited with the built-in flash.
One neat feature that we like about RX100 IV's built-in flash has is that the flash head can be tilted upwards manually using your finger, which can be used to bounce the flash light and create a more pleasing lighting on your subject. It is not a very strong flash so the ceiling/wall or the surface you use for bouncing must be relatively close to the camera.
Focusing
Sony RX100 IV features a Contrast Detection autofocusing system. The AF system has 25 points to choose from. Sony RX100 IV also features
Face detection AF where it intelligently detects the faces in the frame and locks the focus automatically.