completely ignoring the fact that the working class is queer, black, indigenous, not just the domain of cis white dudes.

It doesn't ignore that. The idea is that their issues will also be solved if the material circumstances change and thus it is pointless to do anything about these kinds of issues. Which is basically wrong especially from a tactical perspective but it's not really because they ignore the fact that the working class is also black, queer etc.

It's generally used though as an insult in a really dumb sense though. Often by libs who just throw it around when they want to discard class analysis.