Manufacturing defect has nothing to do with the warranty. The manufacturer's warranty covers only those changes happened after consumer took delivery of it.
Warranties cover manufacturing defects. That's the whole point of a warranty! Once the warranty expires, it's your problem (unless you get an extended warranty). Do you actually expect a manufacturer to cover a car forever?
From the warranty page:
"These warranties cover the repair or replacement necessary to
correct defects in the materials or workmanship of any parts manufactured or supplied by Tesla, which occur under normal use."
From the warranty:
"Subject to separate coverage for certain parts and the exclusions and limitations described in this New Vehicle Limited Warranty, the Basic Vehicle Limited Warranty covers the repair or replacement necessary to
correct defects in the materials or workmanship of any parts manufactured or supplied by Tesla under normal use for a period of 4 years or 50,000 miles(80,000 km), whichever comes first."
https://www.tesla.com/sites/default/files/downloads/tesla-new-vehicle-limited-warranty-en-us.pdf
As for the vent opening, as far as I know, for cars with it, it was open. I haven't seen it being blocked up by foam like in your second picture. Supposedly that vent is used to equalize the pressure in the trunk, so it should be open. Later models removed that vent completely (my 2021 model has metal there).
Pictures of production Model 3s
Edit, from a search. It seems in some cars there was some foam there from factory in 2019. In either case, neither can be considered a defect, but rather just how it was manufactured.
Rear deck cutout
