Digging this one back up one last time for posterity.
There was some news on The Nevers back in November.

HBO and Joss Whedon have parted ways on the production (which will continue without him).
In the CBR article Whedon cites exhaustion and the extra challenges caused by the Covid-19 pandemic. Worth noting how Entertainment Weekly has a slightly different take, noting how the departure aligned with allegations of abusive behavior by Whedon on the set of Justice League (Whedon & Warner Bros. dispute some of those claims).