As far as I can tell this is just a UI bug and does not truly leave those slots open. Known quirk (pun intended): When you use the Quirk Be Gone potion to remove quirks and slots it will still show the circle with the question mark as if they're still open. Without a slot for a quirk to go into, you will never get one. I have edited the action tuning that unlocks the slots for quirks to go into to unlock zero slots, so at fame rank 5 you will still never get quirks. You unlock the first one at rank 1 then another at rank 3 and then unlock the final two slots at fame rank 5. How it works is that there are four slots for fame quirks to occupy which unlock with levels of fame.
This is a simple tuning mod that makes it so you will never unlock fame quirks. No need to do a celebrity cleanse to get the effects of this mod on an existing famous sim now. Just buy one and pick a quirk to remove like normally, but it will now also remove all quirks and lock their slots up so no further quirks can be gained. I have edited the Quirk Be Gone potion from the rewards store to remove all unlocked quirk slots.
