There's not much concrete, but this is a decent summary of the initial accusations.
https://screenrant.com/justice-leagu...ion-explained/
Fisher said that
"Joss Wheadon’s [sic] on-set treatment of the cast and crew of Justice League was gross, abusive, unprofessional, and completely unacceptable. He was enabled, in many ways, by Geoff Johns and Jon Berg." He repeated these accusations in another tweet, saying
"Geoff Johns, Joss Whedon, Jon Berg (and others) grossly abused their power during the uncertainty of AT&T’s merger with Time Warner." When he tried raising these issues at WB, he said that Geoff Johns
"made a thinly veiled threat to my career" Berg then responded that he remembers Fisher not wanting to say the phrase "Booyah". (In a separate interview, Fisher does mention that he didn't want Cyborg "relegated to being the catchphrase spitting ‘cool Black dude’. That’s not anything that I’m interested in watching. It’s definitely not anything I’m interested in portraying.” But Fisher himself never brought that up in the context of these accusations.)
Then WB said they were launching an investigation into these abuse claims, which Fisher seemed happy with. In a social media post, Fisher said he met with their investigator virtually, but had to cut it short in order to double-check certain things with his lawyers, principally that this investigator was indeed independent. He then accused the investigator of not being independent at all, and purposefully ignoring/ghosting witnesses who gave damning statements to WB's HR.
https://twitter.com/ray8fisher/statu...on-response%2F
Now Momoa is backing Fisher, saying
"Serious stuff went down" and claiming that their fake announcement of a Frosty movie starring him was done to distract from his support of Fisher's claims.
So, yeah. Not a whole lot concrete. But we'll have to wait for more details.