Hi,
Secure Boot on arm64 should be working fine with grub2 2.06-9 or later and shim-signed 1.39, both in sid.
If you have SB-capable hardware please give it a try. It should just be a matter of ensuring that your grub-efi-arm64-signed and shim-signed packages are up-to-date. For details about enabling Secure Boot and more information see
https://wiki.debian.org/SecureBoot
Thanks,
ema
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