There are a few accessibility settings you can check for, or get notifications in case these preferences change. This is especially important when developing custom components as they will mostly work with UIKit controls.

Calendar of Advent of iOS Accessibility. Day 21. Honoring users' settings. Display & Text Size Accessibility Settings Screen. There are two examples, Apple's podcast app playing an episode of Swift by Sundell and FaceTime. There are arrows pointing from some of these settings to how they take effect in these apps. When Reduce Transparency is on, in FaceTime you don't see the front camera being previewed and blurred in the background, instead, it is just opaque. When bold text is on, all text in both apps is bold. When Increase Contrast is on, the New FaceTime button is darker. When Button Shapes is on, the button for the podcast show or the playback speed (both consisting of just text with the app's tint color) is underlined so it is easier to be identified as buttons. The sleep timer button, which is an icon, gets some borders around it too. When smart invert is on, the artwork of the podcast doesn't get inverted.