The warning “EFI stub: WARNING: Failed to measure data for event 1: 0x800000000000000b” during Linux Mint boot is a Secure Boot / kernel‑measurement issue that has been appearing across Mint, Ubuntu, Kubuntu, and SuSE systems since 2023. The good news: your system is not damaged, and the boot continues normally. The warning indicates that the EFI stub attempted to measure boot data for TPM/Secure Boot logging and failed.
The most common and confirmed cause is having too many installed kernels.
Multiple independent reports show the warning disappears immediately after removing old kernels.
Then remove old ones using Update Manager → View → Linux kernels.
