Just experienced the same. Latest Kernel for Debian on Raspi 4 renders the device unbootable!
I tried this with 2 different Raspberry 4 4GB but as soon as the Kernel updates to the latest, boot process will stop at:
This also happens on new installs onto a freshly formatted SSD but also with existing installations!
Just avoid updating the kernel (for the time being).
To put the kernel update on hold type the following at the CLI:
sudo apt-mark hold linux-image-arm64
I hope this notice will help others from disaster (luckily I did a full snapshot today)
To avoid “Unattended Upgrades” (if you have that activated) updating the kernel silently in the background do:
sudo nano /etc/apt/apt.conf.d/50unattended-upgrades
Add following into blacklist.
The blacklist section should look like the following: