We deliberately decided against a ventilation system and were able to compare this well because we had a decentralized ventilation in our previous house (built in 2017). The comfort may be good, if you consider it comfortable to have "fresh air" without opening a window. For me, however, this was no replacement for the fresh air that comes in by opening the window. On the contrary, an open window and the sound of birdsong speaks more of comfort to me, but everyone is different. Therefore, the energy-saving effect was lost for us.
The most important point, however, was hygiene. Of course, we regularly changed the filters. Nevertheless, after one year you get a rough idea of what it probably looks like deeper inside the pipes. After another 2 years, I recommend everyone to remove the cover on the duct once and clean through it with a longer object. A joy if someone tends to herpes.
I am now very happy that I no longer have to imagine through which pipes the air comes that I breathe in over several years.
If you google, you almost think you absolutely MUST install a ventilation system. Why? Because those who have one like to make this known. Those who don't have one do not miss it; there simply is no need to philosophize about the fresh air in the house, it is just taken for granted. And: negative opinions are always louder. You will find few posts where someone writes how good their indoor climate is without one.