Prevent sending event registration confirmation emails
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/
HTH
Pradeep