I have to confess I never really know what a "beat" is. (I tend to avoid modern how-to-write books because I am afraid of having the centipede problem. When I played piano I learned by ear, lol.) In screenwriting it seems to mean "a moment," like in older screenplays I've read it goes like this: "KIRK: (A beat.) Do you know what that means, Bones?" Or "Beat. Beat" when the writer wants to indicate that the actors should pause to build the emotional tension. But then "beats" are also individual units of scenes (kind of like atoms?) or the "point" of scenes, like you hit certain beats in action scenes, or in screenplay acts or sequences. That seems to borrow something from music -- they talk about missing beats, or off beats, or whatever. "Beat" seems to mean "Thing that happens?" idk. "Natasha realizes how they can close the portal." "Dr Strange looks at Tony and holds up one finger." I guess I really don't think of plots that incrementally, much less how to deliberately arrange little bits in sequence that way (which is also why I suck at plotting).

(Yeah this is why I don't read how-to writing books, but I love writers writing essays about how they write. I learned most of what I mostly subconsciously know just from....reading a lot, which is also how I learned grammar: I know when something looks wrong, but not necessarily what The Specific Rule is.)