Why can't I add an end screen to my YouTube video?

Usually it’s an eligibility thing, not a broken Studio button. The video has to be at least 25 seconds long, and end screens aren’t available if it’s set as Made for Kids, or if it’s a Flash, mobile-web, or 360 video. If it clears those checks, open the video in YouTube Studio, go to Editor, then choose End screen and add a template or element. The screen can run in the last 5–20 seconds. One extra gotcha: linking to an external website requires being in the YouTube Partner Programme.