I have exactly this setup at my house.
Garage supplied from the house CU via 16mm² SWA and a 50A type C circuit breaker
Shed supplied from garage CU via 6.0mm² SWA and a 32A type B circuit breaker
Shed has 4 final circuits.
1: B20 RCBO socket radial
2: B6 tubular heater
3: B6 inside light
4: B6 outside PIR light
The MCB in the house is B32, the armoured cable then goes to the garage but I have no photo of that CU and didn't look what the rating was when I reset the tripped switch (was too excited to find it ) The garage only has 2 LED bulk head lights and one double socket which occasionally powers a radio. In the shed is one double socket on a B16 (powers a circular saw, sometimes a jigsaw and recharges batteries for power tools). The light is on a B6, but if our solar PIR security outside light outside doesn't work in the darker months then I would like to connect a mains PIR light back to the junction box.
@RF Lighting Looking at your set up above, should the PIR be on a separate circuit?