Is this how most people type on mobile these days, drawing lines all over a keyboard instead of tapping the individual keys? I’ve never had an iPhone so I don’t even know if they can do this natively, but I know you can switch keyboards at least, so it should still be an option if not.
Next time it autocorrects duck or ducking, try a long press on the word and you should get an option to no longer guess that word. Depending on the keyboard you’re using you can typically long press on fuck or fucking and add it to the dictionary as well.
In an unsurprising twist, Gboard doesn’t allow you to dictionary remove duck.
Bunch of gits.