The answer is that there is no set or correct number of beats in a scene. A scene might last seconds or minutes. It could have a single beat or dozens of them. It all comes down to how the scene is constructed and what the intention is behind including it in the script.
So when putting together your own beat sheet, don’t feel limited by number. If you have two beats for a particular scene, that’s okay. If you have twenty, that’s okay, too.
That being said, what can be so useful about a beat sheet before you even get to the screenwriting part of the process is evaluating if those beats actually convey at the most basic level what is supposed to be happening in that scene.
Two beats might be just enough, or you might decide to flesh out that particular scene a bit more. In the same way, twenty beats might be exactly what the next scene needs or you might look at those beats and choose to par down.
Hitting a certain number of beats per scene is not the goal. Hitting exactly the number of beats you need for each scene is.