Depending on what the foam looks like it could mean that coolant is starting to mix with the oil. The most likely culprit for that would be the head gasket. Late model Nissans are known for weak head gaskets.

Stick your finger into oil fill neck. Do you have a milky gunk there too? What about a dipstick? Is there a milky foam ring on it just about inch or so higher than a block casting ends? Did you see this milky gunk there before it got colder outside? If not, it’s probably just cold outside and condensation is not driven off with heat. Engine is not getting hot enough for long enough time. Is coolant still clean and transparent? No bubbles in it? No foam floating around a filler neck?

Anyway, check for blown gasket like others suggest, … but verify above, first. Here in Calgary we have temperatures at - 25C and lower range,  … and if you don’t drive long enough to warm up the engine fully, … or your thermostat rating is just a tad below what it temperature rating should, the result is usually foamy gunk on inside of a oil-fill cap. It’s normal and it will pass as temperatures warm up. Or when you drive more aggressively. Fwiw.

F.S.

Do you drive your car daily/often or once in a blue moon?