I would say what the left needs to do is have class analysis as the central focus, but that analysis cannot be done without also analyzing the effects of racism, sexism, etc. The way those modes of oppression intersect cannot be ignored. Candidly I dismiss post-modernism as largely nonsense, this is most likely due to the fact that my philosophical background is almost entirely in analytic philosophy rather than continental. I also don't have any familiarity with metamodernism or post-post-modernism, so I cannot articulate an educated position on those matters.

So the question should be, "What transcends (to negate and include, to synthesize) both modernism and post-modernism? Post-post modernism is a thing, also called integral theory (based in part on spiral dynamics). Unfortunately, proponents of integral theory don't often talk/write about this level of development through a material/political lens. My fav post-post-modern thinker, Ken Wilber, recently wrote a 50-page or so article entitled "Trump and a post-truth world" which attempts to push past post-modern politics. Def recommend.

Class is an identity and class in this country has been primarily constructed based on identity, and personal experience is a function of material conditions, so these are not mutually exclusive.

Well said, Steve. It seems you are (not for the first time) thinking through at least the theoretical weaknesses of each form of political and economic philosophy. I agree with you that class reductionism seems to deal with the symptoms rather than the cause of prejudicial bias in execution of the philosophy, while identity politics misses the broader picture in favor of an inadequate and myopic self-orientation. But then, what is the "comfortable medium" between the two false directions that captures the true spirit of equality and justice?

So where are we in terms of synthesizing the contradictions between Modernism and Post-Modernism? Where does Metamodernism fit into all this?

A divide in the left exists between what are called class reductionists and those that advocate identity politics. However this really boils down to a deeper divide between two different world views. Modernism and Post-Modernism. Marxism is a Modernist philosophy that seeks to as best we can objectively analyze history and the conflict between classes that drives history forward. Post-Modernism on the other hand denies any sense of objectivity, retreating wholly into the subjective. Rather than analyzing class Post-Modernism takes subjective experience as being the primary focus of analysis. Now clearly there are "class reductionists" that use that view as an excuse to ignore or belittle the effects of racism and misogyny. This is bad. On the other hand there are identity politics advocates who ignore class entirely and focus solely on subjectivity without any broader analysis. This is also bad. However I think post-modernist schools of thought are totally ineffectual at bringing about real revolutionary change. Class analysis is essential to the revolution, although blind class reductionism without any analysis of modes of oppression outside of class is likewise a determent to the revolution. Without class analysis and class consciousness the revolution is dead. Post-Modernism is liberal, particularly in so far as it ignores class. Class is also not an identity, it is a relation to the means of production.