You have to be very very careful with the terms here. What you're referring to here is specifically called High Speed Sync, or HSS, at it is used to sync strobes with cameras above their normal strobe sync speed. Most (but not all) interchangeable lens cameras use what is called a focal plane shutter, which consists of a pair of curtains (on older cameras, it used to be literally a pair of black fabric curtains; nowadays it's lightweight solid blades). When you take a shot, first curtain moves out of the way, exposing the sensor, and when the desired exposure time is finished, the second curtain moves in, cutting off the light. If you're shooting with flash, the flash fires in the interval when both curtains are open. However, because their movement is not instantaneous, if you set your exposure speed faster than a certain model-dependent value, the second curtain will start to close before the first curtain is fully open, creating a strip of light that moves across the sensor - in this mode, the entire sensor is never fully exposed at the same time, so if you fire a flash, part of the image will be dark. To overcome this, you can (but not necessarily want to) use the HSS mode, in which the flash fires a series of high-speed (typically between 10kHz and 40kHz) pulses, creating, effectively, a longer pulse of light that is active while the exposure strip races across the sensor. This allows you to overcome the limitation of normal sync speed, but severely limits the strobe's output power - I can get roughly the same flash exposure using a full dump on my strobes with my lens at f/22 in regular mode, or f/8 in high-speed sync. It is not exclusive to Olympus RC mode, but it does have fairly limited support among underwater strobes - notably, Retra flashes do it with optical triggering (which requires a compatible trigger - it won't work off a camera's pop-up flash or a basic trigger), while Seacam and OneUW do it with electronic sync.
Note that this is very distinct from simply syncing at arbitrary speeds, which is something afforded by cameras with a lens-plane, or leaf shutter - this is typically fixed-lens cameras, although some interchangeable-lens systems also use this type of shutter. Instead of a pair of curtains installed next to the sensor, these cameras use a small leaf shutter installed in the lens, near the entrance pupil, where its range of motion is minimal. This lets them open and close the shutter at extremely high speeds, unattainable by curtain shutters, and thus most compacts can sync with normal strobes (non-HSS) at speeds such as 1/2,000s or 1/4,000s. However, since a full dump of a strobe takes significantly longer than that, it also limits the actual power of a strobe available for a shot.
Finally, there's the Sony's global shutter available in their A9 III camera - this is no shutter at all, but rather the ability to read the entire sensor out simultaneously, instead of line-by-line as is normal in digital cameras. This lets you sync with strobes at absolutely arbitrary shutter speeds, all the way to 1/80,000s, but with the same caveats as leaf shutters.
