Another option is to just connect a Bluetooth keyboard and use hotkeys. You can assign brush and eraser to the same hotkey and then use one button to cycle them. You can actually assign any number of tools to the same hotkey to make arbitrary length cycles, and that order the tools are in on the toolbar will dictate the order in which they cycle.
Any standard Bluetooth keyboard will work for hotkeys. But I use the 8 bit do zero micro game controller for this since it’s easy to hold in one hand, is super portable, and supports keyboard output. If you go for a game controller as an input device, make sure it can output keyboard keys instead of just game inputs. Art studio pro can’t recognize game inputs for hotkeys.
If you are trying to speed up/minimize fatigue using the interface for common actions, I recommend changing the quick menu hotkey to double tap. It’s faster and easier to execute than 4 finger tap. You can put shortcuts to tools in there, it’s faster than reaching to the top since it appears around your finger. I put shortcuts to open the colors, brushes, and layers windows in there, it’s made a significant improvement in speed and minimizing fatigue.