On mobile I access the forum via the DiscourseHub app.
Every other forum uses the following navigation bar. To get back to the main page of DiscourseHub (the screen which lists all your forums) you tap the downward pointing arrow on the right had side.
The Fintechforum navigation bar blocks this bar and as far as I can tell doesn’t provide an alternative way of getting back to the main DiscourseHub main page. As far as I can tell, the only way back is to kill and relaunch the DiscourseHub app.