AFAIK there are no mains powered z-wave/zigbee devices that combine a light dimmer and fan control switch in a single gang footprint.
The fan controller and wall remote that JD linked to is the only device I’m aware of in a single-gang size, but you would need to keep a couple things in mind if that’s the option you decide to pursue.
You’ll need to buy the receiver (which works with both zigbee and 400MHz RF) that is wired into your fan canopy, and the wall remote (which is 400MHz RF only) separately. They aren’t sold together.
You’ll need to do some rewiring at both your fan box and the switch box, since the Hampton bay zigbee receiver requires a single hot wire and then internally controls the current to fan or light. And the wall controller is battery operated, it controls the fan and light via RF communication to the canopy recover, it doesn’t switch the circuit at all and isn’t connected to your house wiring.
All things considered, @rontalley’s suggestion to swap in a 2-gang, new-work box and buy two smart switches might actually be less work and cost.