There is undoubtedly a ton of socialist history regarding the promulgation and study of Esperanto.
https://en.prolewiki.org/wiki/Esperanto
It does not seem like it is nearly as popular as it once was, but there are examples of it being used and even celebrated in Cuba, China, and the DPRK.
I adore the idea of a lingua universalis. I am also aware of many of the criticisms of Esperanto, from its ostensible Eurocentricity to its difficulty with escaping unnecessarily gendered language.
Is there much use in learning it, outside of personal interest or as a hobby? Do you think that there are Esperantist movements large enough to justify learning it? Enough speakers?
Maybe this is a little bit of a cop-out, but I say if you want to learn a language, whether it has a massive community of speakers, small isolated enclaves of speakers, or none at all, you should go ahead and learn it. There’s no real downside unless you factor in the opportunity cost, that being you could have learned another, more “useful” language in the meantime, but would you have done so? Probably not, right? So go ahead and do whatever pleases.
Concerning lingua universalis, I’m not sure if something like that is possible or even desirable. And I’m not sure hand-wringing over “gendered language” or Eurocentricity are worth your trouble either. These are incidental aspects of language, constructed or not. Just my two cents.