Looking for documentation for SSO / Enable Azure Single Sign-on

The helpcenter QTS manual only covers the 3 options on the other tab under ‘Domain Security’

I need to know if local users can be used simultaneously alongside M365 accounts ? for backups rsync/RRTR, ftp, etc there’s not an actual person who would accomplish a microsoft login. And what about an emergency break glass local admin login in case AAD was down or tenant broken ? Or hybrid where some users are in 365 and some just aren’t and never will be.