It's from this page: https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/supporting-documents.html for a visitor visa for a family visit.
I am also confused by the information on the website. IMM 5645 is list as a required form in the website but the new IRCC portal does not require you to submit one.
Does anyone know whether I need to submit a signed IMM 5645 if I use the new portal?