Sounds like sampling bias TBH. The 'far-left' and the 'twitter-left' (or the tik-tok left) are not all quite the same thing either. I don't think you can draw much conclusions about people outside of a platform based on either Twitter or TikTok.

I’ve seen a lot of anti-Israel stuff but I’ve never seen holocaust denial on the far left. What I have seen is an assertion that the holocaust is one of many horrendous genocides that continue to this day, and comparisons between early holocaust actions by nazi germany (ghettos, destruction of the ghettos, resettlement, etc) against the Jews and Israel in Gaza. Personally I think it’s all absurd. The holocaust is uniquely horrific, and every horrific thing doesn’t have to be comparable or have parallels to be horrible. In fact each genocide is its own unique horror, be it in Armenia, Cambodia, etc. Israel and Gaza is also its own situation and the relationships to the holocaust is irrelevant other than in the space of fallacy. The comparison helps no one - left, right, Jew, Palestinian. Every tragedy is its own tragedy and can and should be examined in itself for the lessons they teach, and anyone who uses violence at scale is wrong no matter what happened prior. Perpetuation of industrialized horrors should shame everyone as human beings. But, I was raised Quaker, and we’ve always been persecuted in some way for believing and standing up for the fact you shouldn’t hurt others.

In my many decades as a political observer I have never seen Holocaust denial on the left. I guess it's a pretty niche sub-movement. Where does one pick these nuts?