A little insider info. It’s not just counting cards, it’s more about noticing a pattern. How many face cards vs how many non face cards are played and when. Takes time to notice, but each deck has a pattern. Watch a few games looking for this and you will see.
I learned this by watching my buds play blackjack in Vegas. When you aren’t playing it frees up your mind to see what is going on in the game. The players are too focused to notice what is going on.