Good question! It's mind boggling.
Luckily I came across this 'YouTube workouts' this afternoon on Product Hunt.
A simple platform which helps you discover the best workout videos on Youtube by body part and gender with ease. See a video you like? Add it to your 'Saved' list. Can't find a particular video? Paste the link to add it the YTWorkouts community!
These are free YouTube workout videos, all curated, might well be worth bookmarking. I can already see some winners on there.