Did my profile to this forum get hacked?

when I log in using that profile, I get an option to use passkey. Is that a feature of the updated macOS?

See: Sign in to an account on your Mac with a passkey - Apple Support (Ventura or later)

and: Use passkeys to sign in to apps and websites on iPhone - Apple Support (iOS 16 or later)

The Apple ID shows up twice in the drop down list of Apple IDs when I log in to this site using Safari. One of that Apple ID has a little symbol below it.

Please describe the symbol.

And I'm not able to edit my profile name when I click on Edit Profile & Preferences.

That is as intended. Only the hosts (site administrators) can do so. If you want to contact them regarding your Communities account, see the email address listed in the Terms of Use page.

what does "ASC" stand for?

Short for Apple Support Communities; this site, these forums.

The profile username on ASC can be set when signing up. Any later change can only be done by the website hosts. They might do so on user request, or perhaps if found inappropriate. They would notify the user by email of any change.

Out of curiosity, why do you need more than one?