I tried to follow the instructions in the Moodle Mobile FAQ here, but in Moodle 3.4 there is no Tex Notation filters (Site administration -> Plugins -> Filters -> TeX Notation), only the MathJax filter. It doesn't offer a GIF or SVG output option.
You need to go to Site administration -> Plugins -> Filters -> Manage filters and enable the TeX notation filter first.
Thanks! Missed that entirely.