According to the Ryanair website it states…
- Drones/Quadcopters
Lithium battery operated devices such as drones and quadcopters are accepted for carriage in the cabin once the battery does not exceed 160-watt hours. If the battery exceeds 160 watt-hours, the device cannot be accepted on board the aircraft.
As the Mini 3 Pro battery is listed as 28.4 Wh x3 = 85.2 Wh
So you should be ok