To set the thickness of the pen/highlighter, the manual line space (when you deactivate "Automatic") etc. you have to move a slider to the left/right.
Left to the slider is a number showing the current setting. The number updates, when you move the slider or press on the "minus"/"plus" symbol next to it.

It would be great, if you could add an additional feature, where I can just tap on the number left to the slider and change the value by typing in the desired number.

This would save a lot of time. Specially when you want to set the line space manually, since you often will miss the desired value with the slider and it takes too long by setting the value with the minus/plus symbols.