TOPIC:

When loggin in there is this functionality that shows member names after typing first 4 characters:Enter your E-mail, Name, or Username, then select your Name or Username from the pop-up list that displays.
I don't think it's a good idea - it's leaking the names of all the members, even if they choose not to make their name public.
I didn't find anything in the settings to disable this behaviour.
I would suggest to remove it completely.

The pop-up list that displays is an auto-complete feature in the underlying code.  While yes, it does show names of members who have chosen not to make their profile public (which only shows name and member/officer status as a minimum), I don't see where this is terribly problematic.  Are those members, for whatever reason, totally reluctant to even admit that they are club members?
Yes, you are correct, that there is presently no disable setting, but again, I fail to see how this make-it-faster-and-easier-for-me-to-log-in feature is so troubling.
 

To make it simple - it is not about user's preference - it is a security risk. It allows potential attacker to gather valid user names and then use another attack (ie password staffing) to break into that account.
Do not just believe me - have a look at "Account Enumeration" vulnerability, for example:
owasp.org/www-project-web-security-testi...essable_User_Account
www.virtuesecurity.com/kb/username-enumeration/

Please consider removing it from the code completely.

Your issue has already been addressed. Those who do not want their name exposed can use the Username option.