I had to do this on Reddit over the years. I have zero interest in sport, for example. And it seems there are thousands of individual communities for every sport, every team, all over the world.
I truly don’t care about them, and would like to just block - maybe via a community containing certain words? “Football” for example?
OP mentioned looking for ways to block by certain words, which evidently face the same problem as filtering by keywords, either ways will have risks of catching unintentional topics or just missing them.