Since the word “cult” is usually pejorative, it goes without saying that no professed “Marxist” would say Marxism is a cult.
But is it? What is a “cult,” anyway? Wikipedia’s definition of a cult is
a social group that is defined by its unusual religious, spiritual, or philosophical beliefs, or by its common interest in a particular personality, object, or goal.
By that definition, I would say “Marxism,” as defined by the bullets outlined above, definitely fits the bill.
“social group” - Marxists definitely constitute a social group. They consider non-Marxists to be sinners the same way that Christians or Muslims consider non-believers to be infidels. Some “Marxists” are worse about this than others; but anyone who actually calls himself a “Marxist” definitely behaves in this way, to some extent. He prefers to associate with other “Marxists.”
“unusual… beliefs” - the beliefs of Marxists are not unusual in a historical sense, since Marx mostly regurgitated ancient communist beliefs and values. But they are “unusual” in Western civilization; and they directly oppose Western values of individualism, individual liberty, mutuality, freedom from coercion, etc.
“common interest in a particular… goal” - the goal of all Marxists is to implement a worldwide Marxist (communist) state. Marxism/communism cannot co-exist with another system, at least one that is not equally coercive, since it cannot compete when people are free to choose. This united goal of Marxists is preeminent in their system of beliefs and values. Marx predicted this state would come to exist — and they believe him.
In the past, people like you would use socialist as a weaponised term. Then it was communist, with reds under the beds. Presumably that has lost its punch, with Trump and his cohort consorting with excommunists like Putin. Recently, I read a lot of nutters using 'Marxist' and "Marxism" as their bogeyman, usually, like you, people who know nothing about the economic and philosophical underpinnings of 19th century Marxism, Marx's analysis of class and economics, or class struggle, as he saw it in that century. So, like you, they turn up on you tube and other platforms throwing around terms they don't understand, oblivious to any real study of political philosophy, looking for new ways to project their fears, making false equivalent after false equivalent, and I can't help but think that in the old days idiots would have had to go to a library, take out some books, or study a course on a subject like this, in other words make an effort to acquire some knowledge, but now, with just a few clicks on dumb right wing sites, they can be courageous enough to post their ignorance and stupidity on the online world. It's pity it has to happen on this site as well.