This article is a collection of information and resources for removing the second-row (middle row) seats on the 4th-generation Toyota Sienna (2021-).
2nd-row seats of the previous Sienna generation (2011-2020) were easily removable by pulling a latch. However, the 4th-gen Sienna’s 2nd-row seats are not removable by the user, at least according to Toyota. This is in part because there are now SRS airbags inside the backrests, as seen in this crash test video.
Instead of a quick-release mechanism, the 2nd-row seats are now secured with 4 bolts hidden behind plastic trim pieces. Additionally, the seat airbag connector must be disconnected.
This video shows the process for removing the 2nd-row seats, which involves disconnecting the 12V battery to depower the airbags, prying off seat trim, disconnecting the airbag and seat heater/seatbelt connectors, and removing 4 bolts.