Just to confirm, this is button has been disabled deliberately.
https://community.monzo.com/t/android-beta-1-5-3-update-twilight-app/7851/2?u=alexs
You’ll see this message in the app if you try to tap the button, once the next version of the app is released -
There’s more details on what’s happening from the Monzo team here -
https://community.monzo.com/t/android-beta-1-5-3-update-twilight-app/7851/13?u=alexs