I guess I'd describe repeatedly posting the same emoji to a chat as flooding rather than spamming. Even then, your mention of cheering further divides it into two categories of behavior:

1. Cheering. That's as good a description as any. This is intended to express excitement or approval and rally the in-group. It temporarily makes the chat useless for anything else, but that isn't its purpose.

2. Flooding. This is an intentional denial of service attack intended to make the chat useless for as long as possible, or until some demand made by the attacker is met.

Yeah - one thing I've noticed with some forums is that the addition of the "like/dislike" buttons (some have even more reactions available) greatly INCREASES the signal to noise ratio (I mean makes the forum have more signal, maybe I said it backwards) because the "me too" posts and the "fuck off" posts are reduced, you can just hit the button instead.

Some streaming platforms have a button you can hit that makes party emoji or heart emoji or whatever appear in a stream from the lower right, that's a similar thing which helps with cheering so you can then combat flooding.

I've observed the same with Matrix and Discord. It reduces noise to the point that while "fuck off" would call for moderation in a lot of contexts, reacting with the middle finger emoji usually doesn't even though it has the same meaning.