Cracks/Seams in Moulding - humidity related?

Hi all, saw a few posts like this but am trying to convince the wife these are likely humidity related and not necessarily foundation/“the whole house is falling down!”

Am I correct in my assessment that these are likely due to cold weather here (Alabama so not normally cold) and using the heater regularly?

If these should be sealed, is there a recommended sealant? Caulk, spackle?

TIA!