Have you reinstalled Apricot since you updated FL?
FL Studio only looks for native plugins that were installed for its particular version. Apricot's installer should show the folder (which contains the FL version) that it's being installed for.
You may also need to do a rescan in the plugin manager after you do this.
Let me know if you can't get it working. I haven't upgraded to 21 yet myself, but I know other people have Apricot working with it without problems.