Will they be able to afford their own place and have access to healthcare? I've got siblings that have failed to launch even after several attempts. It's possible this isn't a failure of parenting.

But if it is fixable, you may want to check out William Glasser's writings on the workless (I forget what books of his he writes about it in). Be warned that it's not mainstream psychology and I don't generally think that his views on medication and several other things are good, but the specific ideas about how to deal with a household member that doesn't contribute or take care of themselves might have something useful for you. From what I can remember, it's things like making ingredients available but not prepared foods so they get into the habit of doing things. (Naturally, this is a super bad idea if there's a different issue like depression that should be dealt with first.) That may be difficult to do with apps and streaming services where there's very little between a person and food/entertainment, but you might get some new ideas.