Is it somehow possible to disable invoice for a specific event?
We have an event that is handled by a 3. party who issues the invoice, so we would prefer not sending an invoice to our users for this specific event.
I was considering adding an extra boolean toggle in the tab "Extra information" under the event, with a disable invoice (yes/no). Then add an if/else statement to the pdf function if possible?
Yes. You will need to add a new setting to the event. Then customize the code of the method needInvoice in components/com_eventbooking/helper/registration.php to return false in case invoice is disabled for that event