According to https://help.liferay.com/hc/en-us/articles/360029031791-Configuring-LDAP#general, the LDAP Required check box is described as:
Required: Check this box if LDAP authentication is required. Users can't log in unless they can bind to the LDAP directory successfully. Uncheck this box if users with Liferay DXP accounts but no LDAP accounts can log in.
This implies that only LDAP users can login to Liferay. However, Liferay intentionally allows non-LDAP users with the Administrator role to bypass this requirement, leading to some confusion.
Here is the code that allows this:
To avoid confusion, update this part of the documentation that makes exception for LR Admin users to bypass this requirement.