There are two touch control modes to choose from:

• Point and tap: an immersive mode where there are no buttons on the screen. You tap where you want to go, or on objects or PNJ with which you want to interact.
• Virtual joystick: you can see the joystick, hint, and interact buttons. Please note that there is no fixed joystick option, but you can make the joystick and the buttons invisible in the Options > Controls > Joystick display menu. In this case, use the left part of the screen to move and the right part to interact with objects or PNJ. Long-press to display hints and double-tap to cancel an action.

You can see more in this video: 

You can change the control mode at any time in the Options > Controls menu.

If you're left-handed, you can enable the option "left-handed mode" in the Options > Accessibility menu to invert the controls.

For now, it is not possible to change the size, position and opacity of the buttons and the joystick.