Don't worry about it: Secure Boot is (currently) 100% pointless on Linux because the initrd is not authenticated.
Once the work described at https://lwn.net/Articles/918909/ this will change, and , and kernel updates should no longer require will (hopefully?) no longer require re-initializing the TPM.
Well, all my machines use Arch Linux with custom Secure Boot keys and unified kernel images (essentially, the kernel, the initrd, the command line, and the splash screen fused into one EFI executable and signed as a whole). So on my machines, the initrd is definitely verified. Thanks to Foxboron who made this easy with sbctl.
An entirely different matter is that the default Microsoft keys allow running all other distros, with their GRUB which allows to load initrds without authentication - which would allow evil-made style attacks by replacing the whole boot chain and the kernel. So in my world, all builds of Shim and GRUB are malware, and keys that allow booting them are not allowed in the DB.
Once the work described at https://lwn.net/Articles/918909/ this will change, and , and kernel updates should no longer require will (hopefully?) no longer require re-initializing the TPM.