After a series of firmware updates autofocus and performance of the EOS R have improved significantly.
I was by the water today and managed to snap some birds in flight.
Camera: EOS R with FW 1.6.
Lens: RF 24-105mm at 105mm f4.
Settings on Mode C3 (action):
P Mode, Auto ISO min shutter speed fastest option, Servo AF, Drive mode High Continuous, AF Method Expand AF Area Around, CRaw, Memory card Sandisk 64GB Extreme Pro 170MB/s.