When we register a group of contacts to a Civi event we don't want a confirmation email to be sent (as the registration is for internal purposes). If you register one person at a time the checkbox can be unchecked, but for mass registration this doesn't seem possible. I can see there was an extension back in 2015 which appears to offer the solution but it doesn't appear in my list of extensions now. Is it still valid or is there an alternative solution now? Thanks
If you are on 5.26+ CiviCRM version, when you find contact, select list of contact and use 'Register participants for event' from the action list. It takes you to the Create participant form. When you select the event, there will an option for 'Registration Confirmation and Receipt' at the end of the form where you can select or unselect send receipt option.
You can try on https://dmaster.demo.civicrm.org/