Whatever option you're referring to doesn't show up. It hasn't EVER shown up for me, and I've been trying since you added that part. It's NEVER appeared.
Open the game up in your HTML editor of choice and change the line <<set $GrowthQuests to true>> (in version 0.9.2 it seems to be line 2468) to <<set $GrowthQuest to true>> (remove the S at the end of GrowthQuests), save the file, then restart the game from a new game, or a save before that feature is supposed to unlock (talking to Gwen after getting Ditto to transform for the first time). This should fix the issue you're having; it did for me.
edit: itch.io automatically interprets the less than and greater than HTML codes when you put them in a comment; as far as I can tell, you can't escape that function. You'll have to translate the "<" and ">" back to their character codes to find the line, or just use the line number, or just search for the "set $GrowthQuests to true" part.