At the time of writing (App version 126.96.36.199 being current) it is not possible to change the Mute buttons behaviour.
This means that the individual mute buttons below the faders work as a toggle (on/off) switch and the mute in the bottom right is a Hold switch, and when you release it unmutes.
The idea behind this is so that the Mute in the bottom right can be used if you need to cough/sneeze or have a drink and quickly mute yourself.
This has been reported to the development team as a feature request and we hope to see it in the near future.
Keywords: Toggle, Latch, Mute, Buttons, GoXLR, GoXLR MINI, Go XLR, Go XLR MINI, GO XLR,