I'm surprised this hasn't been reported but searching for macbook, apple and t2 did not yield any results.
Linux is bootable via USB but cannot access the nvme SSD on 2018 apple hardware with the T2 chip.
There is some discussion about the problem here: https://unix.stackexchange.com/questions/463422/how-can-you-get-any-version-of-linux-to-see-the-2018-macbook-pro-ssd and here: https://www.reddit.com/r/macbookpro/comments/92690u/has_any_tried_linux_on_2018_macbook_pro/
There is a windows driver which works so apple aren't completely locking out non MacOS operating systems.
I'm going to close this one. It's not NVMe compliant, hence it won't work with the in-kernel NVMe driver. This is not a Linux bug, it's Apple doing their usual thing. If someone wants to work on this, be my guest.
I would like to reverse the T2 SSD controller’s driver on macOS and Windows. Is it able to finally add support of it to Linux kernel mainline?