Adjacent is falling out of fashion, and ‘next to’ or (for emphasis) ‘right next to’ would be used. ‘Right’ in this usage means immediately or absolutely next to. In the example quoted, which sounds like a user manual, I would prefer to be more precise and say ‘the function is labelled above the button’ (or below, left, right, or wherever)
https://forum.wordreference.com/threads/adjacent-vs-adjacent-to.743723/