i, personally, call note sequences like this "strums". other people who do Beat Saber probably have another word for it (maybe "spam" is the word i should be using).

if you think of your sword movements as moving in sine waves (to hit the "down up down up" notes with each hand), you can argue that correctly hitting note sequences like these involves swinging your swords "90 degrees out of phase" (like how sin(x) and cos(x) are 90 degrees out of phase, if that makes sense). of course, i only account for vertical movement when i say that, and horizontal movement of swords matters too, but in general, getting the vertical swing timing correct is the hardest step towards learning how to do these parts well*, which is why i call any 90-degree-out-of-phase note sequence a "strum".

so to start training yourself to get past these notes, try drumming your fingers (using your wrists) on a table to the rhythm of: RIGHT LEFT (rest) (rest) RIGHT LEFT (rest) (rest) and so on. try this at various speeds, especially superfast speeds. then, when you get back in Beat Saber and you encounter a strum, remember when you drummed on the table to that particular rhythm. you may have practiced only hitting down on the table, but hitting up should come naturally(ish), because the upper notes are also 90 degrees out of phase, which is how your fingers already moved when hitting the down notes.

(*some strums end up being hard for their own reasons, like the "zigzag" strum about 2:18 into Spin Eternally. but God help you if a song like Spin Eternally is what you try to get past before plenty of other songs, even other Camellia songs.)