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BIOS showed the NVMe SSD.
Pressing F3 during boot opened the "Insyde File Explorer", which let me select the debian shim.efi file that booted grub.
Falsche Shim-Signatur (bad shim signature)
Reason: I had manually installed 6.16 to get Debian running on the laptop, see https://community.frame.work/t/tracking-debian-testing-on-the-framework-laptop/14448/34 This kernel had no signature.
This time I wanted to keep secure boot enabled.