All you have to do is type "fucking" ONCE, then tap the word "fucking" in quotes, on the left-hand side of the suggestions/corrections bar, and the word is lear

All you have to do is type "fucking" ONCE, then tap the word "fucking" in quotes, on the left-hand side of the suggestions/corrections bar, and the word is learned as an acceptable dictionary word. Permanently. Forever. And that persists when you change devices. Anyone feigning ignorance of this feature at this point just isn't trying very hard.