Manual:$wgAccountCreationThrottle/en

Details
Limit the number of accounts which may be created within a 24-hour period from a single IP address (whether by unregistered or registered user), 0 to disable.

Account creations from users with the  right aren't counted.

It is currently set to 6 on Wikimedia Foundation wikis. must be set to a value other than  for this setting to work.