After some investigation, we found the problem is that the 250929 firmware does not load the embedded device tree in UEFI properly, while the T2 image does not contain a DTB itself and relies on the firmware provided one.
This has been fixed in the next firmware release. But unfortunately, the next release has updated the embedded DTB to be used with an upcoming v6.17 based Linux kernel. So it will not be compatible with the T2 or earlier images (without specifying devicetree in GRUB2).
However, I think you should be able to see the GRUB menu. Then you can press ‘c’ and type ‘exit’. It will then exit the current GRUB and fallback to launch the GRUB in your SD card.
I just realized that the T2 image uses systemd-boot instead of GRUB2, so the method above won’t work. Sorry for the confusion.