EU situation
Now, as you know, in the EU, everything is aimed towards efficency.
And so are ovens.
An oven has to have at least some way to vent at least a certain percentage of air over time.
First of, air expands when heated.
At 200C (about 390-400F) it is only about 60% the density compared to 20C/68F.
All that expanding air has to go somewhere.
Further, for the most part, you want some moisture to excape the cavity as most baking requires at least some drying to take place.
And - as stupid as it sounds - most want the kitchen to smell somewhat tasty. Not much, just a little, and a completly sealed oven wouldn't smell at all.
BUT you wouldn't want to much air to escape as well to reduce the heating of the room as well as to reduce the energy used and to keep oven temperatures as consitant as possible.
So, the most standard setup is just a small vent section in the top of the oven with a door seal that is pretty much air tight.
On ovens with entirely passive cooling, that is ususally designed to just vent by convetion through a slit over the door in the front.
Most ovens over here however have an active cooling fan by now though.
Those are - mostly - setup with a cooling fan and an airstream divider.
The fan pulls air through the doors which at this point basicly all have at least 2 pains, keeping the front of the door cool enough so you don't burn your hand off completly.
That air is then blown along the bottom of the controls to cool them.
then its passed through the blower and out the front.
On the way out, it passes over a divider under which the oven vent is shielded from the direct air stream.
Thus, the air stream dosen't cause much active air exchange within the cavity and the hot, smelly air gets diluted before exiting the oven.
On earlier generations of self clean ovens, the insulation was often significantly more substantial then on the non self clean versions.
But by now, basicly any oven uses the same thick insulation to cut energy usage, which had the nice side effect of makeing self cleaning ovens more affordable.
Now on to the special cases:
First, ever since the energy label for ovens was introduced, most ovens added some kind of Eco heating settings.
On normal ovens, these heat with greater temperature swings, dimm displays, switch off cvity lights etc.
On some ovens, they are called "Eco" or "Moist" settings. Thus I suppose they somehow alter the venting behaviour as well.
As multi function ovens with full steamers built in became more popular (and mostly cheaper), venting has become more and more of a question.
For example, I know Miele uses a closeable vent on their steam combi ovens.
That opens and closes to keep the moisture in the cavity constant during steam operations, but I bet they close it on any efficency testing as well.
However, I don't see such an item on BSH's exploded views of devices with either steam addition or full steam functionality.
I know that Fisher and Paykel advertised their TOL ovens with a variable vent on launch.
They advertised it for their moist baking settings, but I suppose they use it on self clean modes as well.
Now, self cleaning oven's arent as much of the norm here as they are in the US, but they gain market share damaticly.
They by nature have to seal in more heat while dealing with more heat expansion and even worse smells.
In the early days I am pretty certain catalytic converters on the vents of such ovens were more the norm then anything, both for the US and the EU.
By now, they are somewhat rare.
BSH had that as an option you could retrofit on many if not all self clean ovens of last gen. Only the TOL came with it pre-installed; it was 25€ 4 part thing, two steal mesh sponges, one covered with the catalytic material, in a 2 part holder that would be screwed into the vent divit at the top of the oven IIRC.
It appears incompatible with all current ovens however and even back then basicly nobody used to buy one.
Miele of course takes that to a whole new level.
EVERY pyrolytic oven by Miele does have an AirClean catalytic converter, NONE of the models avaible without self clean does have one. These basic ones are heated by the waste heat of the oven, thus, like on most designs (the old BSH design included) they only get really active during self clean mode.
The highest end ones have a seperatley heated catalytic converter. Thus, any air leaving the oven will always be smell free basicly. The oven control here allows you to choose how much of the cooking smell is supposed to escape the oven in 7 levels.
I have not found any info on the Electrolux side.
I do however think that some TOL brands do have these converters as well - like Gaggenau for example.
For the future, Miele has something interesting coming up.
They are about to launch new ovens with a feature designed to quickly drop the temperature of the cavity if a timed cooking function is selected.
Idea is to quickly drop the temperature to a "keep warm" level so that even if you have a timed function set but walk away, your meal can't overcook.
I could imagine that incorporates a variable vent as well.
