I’m sure there are still a handful of NSFW communities on lemmy.world but I never saw them last very long or remain active. All the one’s I was aware of don’t exist any longer.
I disabled NSFW on my general accounts a few months back because I got tired of seeing the spammers I blocked over here all the time so I can’t help too much for anything new that’s cropped up.
Most forced bi content heavily overlaps with sissy or cuckold content. Depending on where on that spectrum you are maybe that will work for you.
!sissycaptions@lemmynsfw.com
!cuckoldcaptions@lemmynsfw.com