Youtube gives you the option to speed up or slow down your video. This could be helpful for many things. For example, beginners watching this video may slow it down to focus as much as possible. This supports the operable principle.

Many options on Youtube can be controlled by a keyboard instead of a mouse. This is helpful for people who struggle with fine motor. This supports the operable principle.

There are a lot of subtopics or video ideas that are recommended that may become overstimulating. Specifically, people with autism or ADHD. This can go against the understandable principle. Because the video recommendations may seem distracting and messy to some people.

Youtube's layout is simple and easy to follow. There is home, shorts, subscriptions and profile. This supports the understandable principle.

Youtube includes captions on videos. This makes the website more accessible for people who have trouble hearing or can not hear at all. This follows the principle of being perceivable because the instructions of the video are shown visually and verbally. Captions are also helpful in noisy areas or if you want to translate to a different language.