Is the Arhat's Entry into Nirvana Equivalent to Entering the Tathagatagarbha?

The entire seven consciousnesses and five aggregates of an Arhat are born from and sustained by the Tathāgatagarbha. There has never been a single moment when they could exist independently apart from the Tathāgatagarbha. Therefore, an Arhat never exists outside the Tathāgatagarbha, nor can they "enter" the Tathāgatagarbha. If they could, it would imply that an Arhat is also a fundamentally existent, unborn and undying Dharma-body without cause or condition, equating them with the Tathāgatagarbha. Hence, when an Arhat enters nirvana, it does not mean entering the Tathāgatagarbha.

Nirvana is a state where the Tathāgatagarbha exists alone, devoid of the seven consciousnesses and five aggregates. Although in this state only the Tathāgatagarbha exists, with no other dharmas present, it is still the solitary state of the Tathāgatagarbha, uncombined with the seven consciousnesses and five aggregates. If nirvana refers to qualities such as being unborn and undying, neither increasing nor decreasing, pure and undefiled, etc., then the Tathāgatagarbha possesses the nature of nirvana. However, the Tathāgatagarbha is not equivalent to nirvana, because the Tathāgatagarbha has many other qualities and exists in other states; nirvana is not entirely identical to the Tathāgatagarbha. The Tathāgatagarbha is the fundamental nature (essence), while nirvana is a quality and state of that fundamental nature.