Should one have repeated the Maghrib prayer after audibly saying the takbirat al-intiqal to sit for the final tashahhud silently and repeating the tashahhud, knowing that this might be considered a return from a pillar to a non-pillar?

The questioner should be aware that their many previous questions were due to obsessive whispering (waswasa), which they must disregard. As for their new question, their prayer is valid - if Allah Almighty wills - and they do not need to repeat it. It was not appropriate for them to revert to the takbir of transition (takbirat al-intiqal) in an incorrect place, as it is not prescribed for a latecomer (masbuq) who finds the imam sitting. The prescribed action is to say the takbirat al-ihram (definition) (opening takbir) and then sit without any further takbir. Al-Khurashi and Al-Nawawi mentioned in their fiqh books that if a latecomer finds the imam prostrating or bowing, they should say the takbirat al-ihram and then the takbir of transition. However, if they find him sitting in the tashahhud (definition), they should only say the takbirat al-ihram and then sit without any further takbir. Nevertheless, performing the takbir in an incorrect place does not invalidate the prayer or entail any consequence, as it is like other prescribed adhkar (remembrances) if mentioned out of place. The same applies to repeating the tashahhud. Therefore, their prayer is valid, and they do not need to repeat it.