If you are a content creator who uses YouTube Studio to manage your channel, you might have blocked users using the "Hidden Users" list (which is different from standard blocking). However, YouTube Studio also manages comments blocking.
Select (on some versions, this may appear as "Unhide user from my channel"). Managing Your Blocked List
YouTube does not have a central “Blocked Users List” in the main settings menu (like on Twitter or Instagram). Instead, you must unblock someone from the same place where you blocked them: your channel’s Comments section (on desktop) or your account settings (on mobile).