Hello,
the community of de.wikibooks.org decided that MathML / SVG (see https://phabricator.wikimedia.org/T78046 ) should be the default rendering for math formulas (inside <math> tags) for their project. This rendering mode should also be active for not logged in users. Users should still have the possibility to select the PNG rendering mode in [[Special:Preferences]] (before https://phabricator.wikimedia.org/T74240 is implemented).
Greetings,
Stephan Kulla