I used the one from lachlans remake, but FL has an”extract stems from sample” option. You could also use an online stem splitter, or something like izotope rx with music rebalance. U could also try phase cancellation (playing the intrumental inverted against the main signal) but a lot of artists will make changes ti their instrumentals in order to avoid people making clean acapellas. Anyway, izotope rx would be your best bet for a close to clean acapella, but FL’s stem splitter works just fine.