It seems like a good option for those who lost their PR card, however, this will require extra step cause you have to physically mail it to the processing centre... not sure if this will cause reschedule of the Oath ceremony (until they receive the signed document).Sorry I just checked the oath invite again. So you are right you still need to fill out the form if you have not received it. It is the same form if you lost your PR card.
This is the link to the form:
https://www.canada.ca/en/immigration-refugees-citizenship/services/application/application-forms-guides/solemn-declaration-lost-stolen-destroyed-never-received-permanent-resident-card.html