Mine are
Selector button set to: FN
Fn1: previewEXP./WB ON manual
I have to disable exposure preview only when using strobes.
Fn2 / UP button: ISO
Using to change ISO often.
Fn3 /LEFT button: FACE/EYE DETECTION SETTINGS
This will help enabling eye focus only when needed.
FN4 / Right button : SHUTTER TYPE
Typically I shot in electronic shutter. I will select mechanical only when that is necessary via this button. Specially when using flash, florescent lighting as well as fast moving objects.
FN5 / DOWN button: focus AREA
This was default. I use this button to change focus points. I also have touch screen focusing point change enabled.
AE-L :AF MODE
Typically I shoot single point. But if I'm to shoot moving subject mostly I'll change it to zone via this button.
AF-L: AF ON
I have AF removed from shutter. I use back button focusing with this button
REAR DIAL FOCUS CHECK
Default
I would like to see what you have assigned in your x-t20