@valpis : I think there is full explanations in the PPR letter you have received. PR visa will be issued by the local visa office (normally within Embassies or High Commissions) where it was processed. However, check the travel restrictions due to COVID to Canada and from the country where your mom is residing.
"visa required > via visa office VS. visa not required > send directly to Warsaw"
I am also not clear about this but this may be due to Warsaw Visa Office serving to other countries where visa is required to come to Poland?
As you have said that there are Visa Application Centers where Embassy is not located.