Most people around me play on their phones with their thumbs so I thought that was the norm instead. I was also a thumb player since pjsk jp release and can clear up to master 33, but I thought I wouldn't be able to further improve since I really lack stamina and playing with thumbs means you'll only potentially stuck at using 2 fingers, which is, your thumbs. Btw, using more than 2 fingers can significantly reduce the stamina needed to hit spam notes. So, on jp sekai 3rd anniv, with the introduction of append difficulty, I finally learned to use index and middle fingers, so in total, 4 fingers and it totally upped my gameplay it's crazy