Yes there is a capacitor, yes he rotates the voltage / current, but that does not mean that the result is rotated by 90 st and the ZCD will detect a voltage peak
Her is simulation on my design
Red is voltage 230V
Green output of optocoupler
Yellow is current over LED in OC
Blue current over second LED in OC
The circuit detects a zero of about 1500 us over a true zero
Her is same only with 2x 35k resistor
The circuit detects zero about 1500 us after true zero
Yes both for LED current 5mA
Consumption circuits approx. 750mW against 35mW with C + R
Her is precise and complicated
ZCD
Detection exceeds zero by about 500us
Consumption about 180mW ,but 13 components , in longlife and SMD 15 becouse R1 and R2 it is advisable to always replace the pair 1206 4x 110k (voltage stress)
Do I see something wrong?