Playing Pico8 games on mobile phones - while very convenient - has its issues, the major one being the the lack of tactile feedback you would expect from hardware. This tends to make my thumbs lose track of where the buttons are when I focus on the playing screen. Games like Celeste that require quick and precise button presses tend to be unavoidably more difficult to play on mobile.

To lessen the problem, I think expanding the directional key area would help, mainly with the top-left(green), top(blue) and top-right(red) keys as that's where I believe thumbs get lost the most.

The horizontal view gives the directional keys more room and doesn't interfere with the X O keys, so the right and bottom-right keys could also potentially be expanded.