Linux Mint has a different password strength requirement to generate a valid (not "weak") password to enroll secure boot and to create a user password.
For instance, I can use a password of 6 characters with only numbers for the user creation screen, whereas I can't do the same for the secure boot screen (together with multimedia codecs).
This is a limitation of the installer, because I can use the mokutil command in the terminal to create a test password of 6 characters with only numbers for secure boot integration (MOK enrollment).
Thanks for your attention.