Here is the 2020-2024 Model Y manual's instructions on opening the back door with power loss, doesn't seem that obvious to me (you have to "remove the mat from the bottom of the rear door pocket" !): https://www.tesla.com/ownersmanual/2020_2024_modely/en_us/GU...

At least on the newer ones it looks like it at least has signage and is less obstructed: https://www.tesla.com/ownersmanual/modely/en_us/GUID-A7A60DC...