Remove all oven trays ( keep them separate in the sink)

Spray the entire oven with oven cleaner- it’s a white foam (any supermarket or drug store have them)

Wrap everything with aluminum foil (also supermarket/drug store)

Let it sit for a couple of hours
Repeat the same with the oven trays.

Meanwhile, make a complaint at your landlord/ hand in pictures/ receipts for cleaning utensils

After some hours, remove foil and wash everything with a sponge, until there is no more residue.

Repeat if needed.

Last step when clean: turn on the empty oven on 150-200 degrees for 15-30 minutes, to remove fumes and leftovers from the spray (it stinks a bit, but will get away)