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“Something has gone seriously wrong,” dual-boot systems warn after Microsoft update
(arstechnica.com)
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I was interested too. It seems Microsoft has released a patch that blacklists vulnerable grub versions from being able to be secure booted even if they are signed properly:
https://msrc.microsoft.com/update-guide/en-US/advisory/CVE-2022-2601
The link was at the top of the article.
Maybe this update somehow affects your UEFI firmware, and it installs a list in there?