So he's been normal throughout your marriage, but 'lately' [this week, month, year] started gagging and commenting on normal cooking smells.
With the gagging, with a woman, I would say, 'Is she pregnant?'
With a man there are only three options. 1 that something rare and medical has rapidly developed. Or 2.; That he has a psychological problem making him gag involuntarily. Or 3. he's doing it deliberately .
In any case, it is above Mumsnet's paygrade.
He won't have a reasonable conversation about it. So your first step is to rule out a genuine medical reason. Maybe gagging at smells is a symptom of something.(A) consult a doctor to find out if it could have a physical cause. The way one smells burnt toast when having a stroke. E.g. something like a tumor in the area of his brain perceiving smell has developed, or if it's a symptom of something, like pain in your shoulder means something is wrong with your liver or wherever.
If he is cleared by a doctor, then:
(B) A therapist to get to the bottom of why he's doing this. An involuntary reaction, e.g. Some childhood trauma or whatever, or (C) Is he just being a dick to make your life difficult for some reason.
The outcomes will be (i) he stops it, (ii) he doesn't. Then it's for you to decide to (I) live like that forever, (II) stick around in the hope it stops.