I am using my phone mostly with the left hand and therefore have to reach over with my thumb to hit the smart button.
Some ideas that might help left handed users:
Maybe you can make the position of the smart button customizable (left, middle, center). The Reddit app allows to put their reply button (similar to the GoodTask smart button) anywhere on the screen by touch-dragging it. Won't work right now as the long touch is already in use but still maybe something to consider.
If the smart button cannot be changed, can you maybe extend the touch targets for all the options all the way to the left. This way even though I have to reach over to hit the smart button on the right I can slide back to the left while selecting an option. (It gets tougher to reach over with the thumb the higher on the screen I get, hope that makes sense