lk/fundamentals/pam.md

The Pluggabble Authentication Module controls minimum security requirements, such as password lengths.

Configuration rests in /etc/pam.d/common-password, or sometimes system-auth.

The file might be edited to contain:

password required pam_cracklib.so minlen=12 lcredit=1 
 
ucredit=1 dcredit=2 ocredit=1 

This would enforce a minimum length of 12 characters for a password, one lowercase character, one upper case character, two digits, and one other (special) character.