First off, why tf are you even attempting to use Flapple in gen eight ou? That mon is straight up hot trash. Don't use it. Second, you're better off using Clefable. Most non fully evolved Pokemon are not useful in ou because everybody and their mothers love to spam that brainless move called knock off and Clefairy is just as trash as Flapple if its eviolite gets knocked off. Clefairy isn't even ranked in the vr for that very reason. The only eviolite Pokemon that is even remotely viable in ou but not in the rankings is Chansey and the blob is only used by guys who have no life at all and want to waste someone's time on the ladder with a super hardcore stall team because they have nothing better to do
If someone says they're using Clefairy, then there's only two reasons for that. One, they're probably in the low ladder which is around >1400 elo and don't know much about the metagame or two, they have a very specific purpose in mind like using it against a specific player in a tournament because that player plays in a style which Clefairy would be more useful than Clefable. This second reason would only apply to that specific player and nowhere else especially on the ladder
In the end, don't use Flapple because it sucks so much balls and don't use Clefairy because it's even worse the moment its eviolite gets knocked off. In general, using Pokemon that rely on eviolite is not worth using in ou. Remember, everyone and their mothers love spamming knock off