I have been using a Lenovo Ideapad 3 (Lick) with Coreboot and PopOS installed for a couple of years without issue (it runs much better than my more powerful Windows PC I use for work).
I recently received a prompt to update system firmware UEFI dbx, however I wonder if I should proceed as I originally flashed the firmware from MrChromebox guide and I would not wish to damage my system,
the UEFI secureboot revocation database (DBX) is an updatable component of the UEFI firmware that tells secureboot what signed EFI executables not to trust anymore. It’s designed to be updated independently of the main firmware, but MrChromebox firmware does not support this feature at the current time. You can ignore for now and the next MrChromebox update will include an updated DBX.