Designing and building so that people with visual, motor, hearing, or cognitive impairments can use the product: keyboard navigation, screen reader support, sufficient contrast, and clear labels.
It is a legal requirement in many markets and a commercial one everywhere: roughly one in six people has some form of disability, and the same fixes improve usability for everyone on a phone in bright sunlight.
We use semantic markup, keep every interactive element reachable by keyboard, check contrast during design rather than after, and test key flows with a screen reader before release.