UEFI Secure Boot on the Raspberry Pi
A port of the free software TianoCore UEFI firmware can be used instead of the proprietary boot blob to boot the Raspberry Pi. This allows to install Debian on the RPi with the standard Debian Installer, and it also makes it possible to use UEFI Secure Boot. Note that Secure Boot had been broken on arm64 for a while, but it’s now working in Bookworm!.
Source: UEFI Secure Boot on the Raspberry Pi, an article by Emanuele Rocca.