You can block users on Twitter, yes. In fact, in some circles, "block chains" (no relation to the crypto-related tech) are popular; the idea being that you use a script to not only block one person, but subsequently block everyone that follows or is followed by that person, then block those that follow or are followed by those people, and so on to a certain level of depth - kind of a "curse you and your offspring for ten generations" sort of vibe. I suppose in a way this is functionally similar to blocking an entire instance on the fediverse.

Not sure if you can block hashtags or something like that on Twitter.