I’ve been asked by one of our users to increase the text size of our instance. Fortunately, this is easy to do for her personally using the interface settings (see https://meta.discourse.org/my/preferences/interface).
She tells me that other sites and apps have the ability to do this automatically if the device has a large font selected.
Discourse used to have dark mode being user-selectable only but this has changed in the last year to be automated (if configured correctly). It would be brilliant to have the same dynamic for text size. Indeed, this is far more important, as visually impaired folk will struggle to find the setting with the text being small.