Anja I make yoghurt in my Instant Pot - like you, just milk and yoghurt, nothing else. It really is the best, isn't it? Can I give you tip? If you use UHT milk, there's no need to heat the milk to 82deg first, just to 43deg then turn off, so no waiting around for it to cool.
Also you don't need that much yoghurt as a starter either. I use just one rounded dessertspoon of yoghurt with 2 ltrs of UHT milk. Using too much starter can actually be detrimental, something to do with the two main cultures fighting each other for the available food. This really went against the grain with me when I first read about it, because I'd been making yoghurt for years in a 7 pot yoghurt maker, using a whole tub of yoghurt to one litre of milk. Sometimes it worked well, other times not so well. Since I've been using less starter it never fails!