We have enough datapoints to say that most of the time instant-unconscious seems to be an intended possibility, the language involves some form of stealing the air. Usually as a Crit Fail to a save.
Though there are also crit fail effects in that list that just say "the target falls unconscious and starts suffocating". These also seem to skip to the second paragraph of the suffocating rules.
Aside from the obvious outlier and oddly written R2 Choker, the only one I can see like that is Kurobozu.
The Crit Fail does jump right to "As failure, plus the creature falls unconscious and begins suffocating."
though hilariously enough, the "involves some form of stealing air" is still true for that creature due to the context, and even name, of that ability.
Steal Breath [two-actions] (incapacitation, necromancy, occult)
Requirements: The kurobozu is adjacent to a living creature that is paralyzed, slowed, stunned, or unconscious;Effect: The kurobozu leans over and sucks the breath from the target, who must attempt a DC 22 Fortitude save. Regardless of the result, the creature is exposed to black apoxia and its breath reeks of carrion for 1 minute.
Critical Success: The creature is unaffected.
Success: The creature can't speak for 1 minute.
Failure: The creature becomes sickened 2 and can't speak for 1 minute.
Critical Failure: As failure, plus the creature falls unconscious and begins suffocating.
So not only is that R6 creature's ability got the incap trait, but it's got a contextual requirement of an existing affliction before it can even use it, and the ability only manages to completely steal breath on the crit fail.
Even in that example, it still is great supporting evidence that the "instant no save suffocating" effects like that of the Choker are big outliers/errors that likely meant to invoke "can't breathe," and that most of the time suffocation seems intended, there's air being stolen/removed.
Sarglagon's crit fail Drown effect also doesn't say it depletes air, but it does refer to Fortitude saves vs suffocation that the effect presumes the target is making.
Drown [two-actions] (divine, incapacitation, water) The sarglagon conjures murky water to fill the lungs of a creature within 30 feet of it that can't breathe water. The target must attempt a DC 26 Fortitude save.
Still removes air indirectly via water-filling.
The water filling happens on any result short of a critical success, with varying ways the water can be expelled.