After the terrible experience with my dealer (Bílaumboðið Askaj), I had to investigate whether they did at least installed all the firmware updates needed to make drive battery pre-conditioning work:

While the Kia (and Hyundai) EVs always had a "winter mode" where it heats the drive battery up to +5 °C when it is below -5 °C (and the battery has a low SoC, i.e. it can be anticipated that some charging might happen soon), recently heating to reach 20 °C has been added by selecting a High-Power Charger (HPC) with a power of 150 kW or more or a slower DC (i.e. <150 kW) charger. This can be annoying if outdated map data indicates no charger to select in the navigation system that you can set as destination or waypoint -- but in that case, just claim to navigate to the closest DC/HPC charger known in the map.

However, to make that work, you need

1. Navigation/infotainment system update for the head unit (HU), e.g. the one from Dec 2022 (you can do this update on your own)
2. Update of ECU firmware (BMS and VCU) -- only the dealer service can do that

You still have the old winter mode, if you see in your head unit in the "EV settings" section an entry "Winter mode". If you see rather instead "Battery conditioning mode", then you have the new battery heating mode:

The conditions to activate are not fully clear, but my summary of the best forum post (in German) on that topic that I found so far is:

1. Of course, the new "Battery conditioning mode" needs to be enabled
2. Navigating to an HPC/DC charger (note: it is often written that this needs to be an HPC charger, but I experienced that a DC charger also activates battery heating in cold condition), even as a waypoint -- but be aware that navigation only starts if the HPC/DC charger is the very next waypoint (in case you have multiple waypoints).
3. Drive battery temperature below 21 °C (heating will later stop once 21 °C or more have been reached, but will resume again once dropped to 19.5 °C or lower)
4. SoC is 24% or higher (heating will later stop once SoC is 20% or lower) -- somewhat stupid: optimal charging speed means to reach the charger with an SoC as low as, e.g., 10%, but battery heating is not possible with low SoC
5. It is not fully clear, when the preconditioning starts: it seems that it depends on the temperature of the battery (the colder, the earlier the preheating has to start). Also, it seems that preconditioning stops somewhat before reaching the charger (in order to spread or balance the heat inside the battery to prevent that some modules are too hot while others are too cold): a hypothesis is that the car estimates the SoC that it will have when it arrives at the charger and stops at a Soc that is 10 percentage points higher than the estimated SoC of arrival (this would fit to the fact that preconditioning stops at 20% SoC as the car estimates then to arrive with 10% SoC, i.e. leaves another 10% SoC as safety buffer).
   
   It seems that 10 minutes of pre-conditioning increase the battery temperature by ca. 3 Kelvin (in -4°C, my car started heating 70 minutes in advance of reaching the HPC charger).

You will notice that the battery heating is active if a snow flake (model year 2022) or a heating spiral icon (model year 2023 -- this is related to the firmware used by the cluster unit (CLU) firmware that displays the main dashboard) is shown in the battery percentage bar on the very bottom left of the dashboard.

Also pre-conditioning (to +10 °C only, though) via app is possible by either simply starting climate control for the cabin or by setting a schedule for climate control (i.e. not only the cabin gets heated, but also the battery -- you can use this, e.g., if you have the car parked at home and want to fast charge at a charger very close to you: in this case, the pre-conditioning during driving would not be long enough; but if you do not intend to charge, but only want to pre-heat the cabin, heating the battery wastes of course energy):

1. Activated pre-conditioning via app
2. SoC at least 35% (this is what you read in the forums, I had the feeling that this percentage might be even higher)
3. Drive battery temperature 8 °C or lower
4. Every pre-conditioning as part of a 15 minute cabin pre-heating increases the battery temperature by ca. 5 Kelvin

The app indicates this (in the European app, next to the battery level bar, is a question mark icon: if you click on it, it shows how battery pre-conditioning will be shown in the app). Just be aware that the conditioning needs ca. 1 minute to start, so you will not see it immediately (e.g. in the app, you need the refresh the status after ca. 1 minute in order to see the changed battery icon).

In the charging curve below, you find a good overview on the charging power in relation to the battery temperature. Many forum posts support that there are 5 Kelvin steps (instead of a gradual curve) and of course, it depends on the state of charge:

Note also that both the coldest and the warmest battery module needs to be within that temperature range.