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Sure but calling someone an idealist is something a non-marxist boomer could say (in the non philosophical sense). You have to have Marxist brain worms to say revisionist.

Then I thank you for the clarification.

Where would you say "realist" exists in this context?

I'm not the OP, but I would like to speak on this matter and, perhaps get some relevant input.

That seems to be a roughly correct assessment of what idealism is if we replace the word 'reality' with 'material part of reality' (because non-material part of reality is still a part of reality). However, I see a couple of issues with the assessment of Marxism as supposedly being a materialist and anti-idealist school of thought:

1. I'm not sure what the argument is for how the ideas encountered in math depend on material part of reality. There is no such dependency as far as I can see as a person with a background in mathematics.

2. I am not aware of any Marxist positions that are in conflict with idealism. If there are such positions, I'm all ears.

thank you, you are completely correct. more marxists need to understand that idealism is the opposite of materialism.

it is incompatible with Marxism as idealism is the opposite of materialism and Marxism is rooted in materialism, not idealism

I have to disagree. Marxism does not seem to be rooted in either materialism or idealism, or, at least, I do not see any contradictions with either. A lot of people seem to hold this view out of gross misunderstanding of what idealism and materialism (as well as the relevant types of those, such as, for example, ontological idealism and materialism) are, and an assumption that idealism is some sort of a belief in magic.

Like, one of the schools of thought that I subscribe to is mathematical Platonism (perhaps with some modifications, as I have not seen any mention of concepts such as what I describe as 'manifestations of ideas' in sources regarding mathematical Platonism), which makes me an idealist in the ontological sense. In what ways are those views of mine incompatible with Marxism? I see no conflicts of any sort of significance whatsoever. I do not think that Marxism has any sort of dependency on ontology, or, at least, I do not see those dependencies.

Capitalism, value, and social stuff can be analyzed from an idealist perspective, but a Marxist would analyze those things from a materialist perspective

If we are talking about strict materialism, then such perspectives would posit that non-material things do not exist, and I am yet to find a Marxist who holds those views.
If we are talking about non-strict materialism, where non-material things can be said to exist, then how do those perspectives differ from idealist ones in this context? I do not see any dependencies of, say, Marx talking about various forms of values of commodities on making non-strict materialist assumptions.

They don't merely exist as ideas, but also as real material institutions that have material affects on people

However, that is not in conflict with idealism, and, furthermore, when relevant things are discussed in socialist spaces, including Marxist and Marxist-adjacent ones, people almost always talk about the non-material stuff. Not to the exclusion of material things, of course, like people getting sick, or some goods or materials being moved to somewhere, etc., but people also talk about and in terms of stuff like capitalists and workers' relations to capital, land, and labour, like laws being passed, enforced, and abolished, like policies of various states and organisations, etc.
And, of course, I am yet to encounter any sort of Marxist perspective where materialist assumptions are necessary, unless I am missing something.

None of those things you mentioned are non material

None of those things consist of any matter. They are not material things. They have connections to material stuff, but they are not themselves such.
Furthermore, when discussing, for example, social relations, people very rarely talk about the material stuff, and, indeed, we usually do not have much of an idea of the configurations of the brains of relevant people, or about other relevant material stuff. That does not impede us from, well, discussing those.

The problem then with idealism is that if you don’t understand how concepts like capitalism are embedded in the physical world, you are very unlikely to understand how to change them

Understanding connections between capitalism-as-an-idea and material stuff, including what I would describe as manifestations of capitalism, creates no conflict with idealism, though.