Theoretically you could cut the time you spend drawing portrait in Procreate by half by activating ’Drawing assist’ mode, in this case everything that I drew on the right half of the screen was mirrored on the left. In reality faces are rarely perfectly symmetrical so you’d keep turning off drawing assist to add any asymmetrical features.
As this is practice on my Introduction to Procreate course, I stayed in ‘Drawing assist’ for the whole drawing.