One thing that I think isn’t exclusive to ultraleftists but which is a very influential force in ultraleftism is a purity fetish:

This article on the topic is a banger and it should be mandatory reading for everyone in the radical left.

I think that ultras are a lot like trots in how they essentially believe that you have to arrive at an immaculate position by divining the meaning of Marxist texts in order to achieve The Correct Position™, rather than actually rolling up your sleeves and doing the work to implement theory and to address the inherent contradictions as they emerge in order to make change.

I also think that ultras have a similar tendency to some anarchists in that they adopt an ideological position of negation (and in the case of ultras especially, an intellectual position of negation too) where they can immediately dismiss attempts at revolution or achieving socialism as being somehow insufficient. In some anarchists, you see that with them immediately denouncing anything as “authoritarianism” and ultras take a similar mental shortcut except they use more words and quote more theory. “Hmph, you support Cuba? Read Bordiga’s [whatever] and you’ll understand why you are wrong, loser.”

Honestly so much of it just comes off as cope to me.

Fortunately the price of admission for being an ultraleftist is high - you need to read a lot of theory, the movement is incredibly fractious (mostly because they aren’t focusing on achieving an actual, practical outcome through collaboration, and without that people tend to descend into petty bickering rather than developing community and learning to overcome differences through striving together to achieve the same thing), and they have basically relegated themselves to being above it all and separate from it all.

This means they’re pretty inconsequential and they’re always going to be a fringe element because so much of their, whatever, identity/political position/project is invested in what is essentially armchair quarterbacking (pun intended) and thus they opt to be sidelined as a necessary precondition of being an ultraleftist. When I encounter them I pay them no mind.