In addition to being able to test some accessibility options in the simulator using Environment Overrides. You can even preview some of these options before even running the app in the simulator with this Accessibility panel in Interface Builder.

In Interface Builder in Xcode, there are a few options for tweaking how your UI looks in it including Appearance (for dark and light mode) and orientation. But also an Accessibility option that shows a panel where you can set Interface Builder to show everything in a non-default Dynamic Type text size, Bold Text, Button Shapes, On/Off Labels, Increase Contrast, and Reduce Transparency.