The average pubg player will most likely use just both their thumbs to play pubg mobile. But, a lot of "above average" players add up fingers to get a faster and accurate gameplay, starting from 3 fingers, heck, I've even seen 10 fingers you kidding? Anyway, how many?
Not the fingers, but the skills and your reflexes matter the most
Personally i play on 5 finger setup, my friend who is a 2 finger thumb player plays as good as me..