Are such projects usually also advertised by the city, or do you rather look directly through the developers? I see stuff like that now and then on the portals and have occasionally gone to the developers’ homepages, where I then found other potentially interesting things. Sometimes the sales then also run through third parties. Are there actually common outlets where you can find such projects? Or as always, Google is my friend and otherwise just contact the sales departments?
I’m not exactly sure what you mean by "such projects."
The city/municipality rarely builds houses and markets them itself. But of course, they often provide information about new development areas. And the city/municipality decides on the type of houses through the zoning plan.
And then there is, of course, the case where larger private plots are divided and a sort of mini new development area arises.
If the plots go to a developer, you will ultimately find it there. Sometimes these are newly founded companies that deal only with marketing the development area. You cannot have them on your radar beforehand.
In short: you will not find a portal that clearly displays all new development areas with a link to the seller.
You will have to keep your eyes open in all directions. After a few weeks, you will notice that you have an overview from several sources about what is planned where and when. And the sources will complement and overlap each other: info from the official municipal site about planned new development areas, articles from the local newspaper about protests/citizens’ meetings/city council meetings, info from marketing pages of the developers.