I don’t think Jenny is on Nebula. She’s got a patreon where she releases smaller videos every month, but to my knowledge she’s never “left” YouTube - she just takes a long time to create and edit these videos so she can only release them pretty infrequently. She’s got a comment pinned on this video saying about as much.

Are you thinking of Lindsay Ellis? She’s still Nebula (and maybe patreon) exclusive.