"I don’t understand why Palestinian supporters in this country rarely denounce Hamas."
Usually because they've taken up a binary viewpoint, e.g., they view the IDF a immoral and cannot then denounce Hamas due to their binary thinking.
This is highly common behaviour not just amongst those who are terrorist supporters and fellow travellers, but also amongst the sneaking regarders. Speed & willingness to deflect from a terrorist organisation in order to focus on a Sovereign Government is a sign of a sneaking regarder, for example.
Another would be they don't really know very much about what Hamas does, how they think, how they operate, how they manipulate people and so on. Its not simple or straightforward, so they far prefer the more simplistic narrative regarding the IDF that's pushed routinely.
As we've seen recently from the United States, Iran has been using paid activists in the US to foment what we've been seeing there. The same kind of thing has been going on in various European States too.
https://www.dni.gov/index.php/newsroom/press-releases/press-releases-2024/3842-statement-from-director-of-national-intelligence-avril-haines-on-recent-iranian-influence-efforts
So, there will be multiple reasons why Westerners aren't denouncing Hamas at these protests. Little of it good.