Is it possible to create buffet worlds with Multiverse, and to be more specific, create buffet worlds with the Multiverse API?

Just adding a 👍 here. I'd really love to create a single biome world without having to resort to a custom world generator. I want the world to be as vanilla as possible . . . just with one biome.

Not currently, and possibly not in the future. It seems it was removed from the Spigot API as of 1.16, although, it was present in 1.15. It's possible they moved it to another package, so I'll update you here if I find anything out.

I noticed that as well, but I was just wondering if Multiverse had another system. If we can't find anything, I'll make my own generator or switch the api to 1.15.

Hmm, I've been able to trace the removal back to here.
The commit's description is "Update to Minecraft 1.16.1," which gives me a suspicion that support for this world type was removed from the 1.16 server. This seems really odd, though, as the Buffet world type was merely renamed to "Single Biome" in 1.16. Unless they changed how it works internally, that makes no sense.
If the removal was simply because they've changed how it works, then I feel like it's only a matter of time until it's back. Possibly Multiverse could find a workaround? I've noticed that this issue's milestone has been set to Multiverse Next so that gives me a little bit of hope for that.