I built and installed kernels 6.12.1, 6.12.43, 6.12.48, and 6.11.11 — Debian booted correctly on all of them. Then I rebuilt kernel 6.12.43 using the Debian kernel config taken from /boot of the kernel from Debian repos, and Debian failed to boot with exactly the same symptoms as the original kernel. That means the problem is in the Debian kernel config. I’m attaching a git repository with the kernel configs: https://codeberg.org/johndoe9232/debian-bug-1114695.
I can’t promise, but if I have time I’ll try to find the config option that causes the boot hang. If it's important, without "quiet" option I only saw "EFI stub: Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path" message.
