I have the sane issue where I couldn't select anything in the menu . I accidently turned off the mobile buttons option and now I can't play at all because back buttons don't appear and I can't turn it back on.
I found out that to "back" you need to tap with 2 fingers. In the menu, you tap the section you want first until it stops blinking. Then its sub will blink and you can start choosing.
For example, if I want to see character skill, I need to tap with 2 fingers to open menu, click on skill twice, and click character twice.