As expected, grass, tall grass, and ferns have a chance to drop wheat seeds when broken in survival mode. However, large ferns apparently do not drop seeds; I have broken dozens upon dozens in survival mode, and either I'm incredibly unlucky, or large ferns have a 0% chance to drop wheat seeds. Is this a bug, or are small ferns not supposed to drop wheat seeds even, as they were renamed from "seeds" to "wheat weeds"?
Can confirm, the loot table does not include wheat seeds, as opposed to small ferns. This is also the case in 1.14.4, so it might be an older issue.