That’s one of the frustrating things about the ST app. Although the ability to operate a capability may be exposed, it might not be exposed for automations. As Andreas points out, you can see the list of capabilities for your device on the ST Advanced Web App. If you see a capability for the vent fan in the AWA, it will likely be available in 3rd party rules engine sharptools.io. You can either 1) write a rule in sharptools that is triggered when the range is turned on; or 2) create a virtual device in ST to be a proxy for the vent fan in sharptools and write a ST Routine that is triggered when the range is turned on with an action to turn on the virtual fan. Then have a sharptools rule that mirrors the status of the virtual vent fan to the actual vent fan capability.
On mine, through the ST device I can adjust the fan (all speeds), but in the routine only the low speed and on/off is available. I think this illustrates the point that the device and automations don’t align as you would expect them too. What I’ve been looking for is the ability (on my oven) for the eco setting to turn the display off automatically, which I can physically do. This is not available in either the ST device or automations, although it is something that would logically be exposed for ST as you could schedule it off at night.
As I said, for some reason, Samsung has chosen not to expose all the capabilities of the device in the automations/Routines. My suggestion is to look at using a tool like sharptools to achieve what you want.