Just to note, hiding them using CSS wouldn’t disable Likes/Reactions, and could be sidestepped in the browser console or by using safe mode (may be relevant depending on how troublesome the user in question felt that day )
However, I think the question is how to disable other people from being able to Like/React to a specific user’s posts:
The goal is really “don’t feed the troll” as the individual in question loves to take the counterpoint in discussions, be contentious, and in general hasn’t found an internet hill they are unwilling to die on.
The tough part is generally speaking they contribute positively when they initiate a topic or post. The challenge is how they choose to respond to others.
My rationale is if I can deny the dopamine of likes/reactions maybe the behaviour changes.