There I just have one project for each … project because they are separated.
I just saw that something like that works in Zitadel too, so I only have to run one instance. But is this meant to work like that? Or should I rather spin up one instance per project?
We support multiple approaches for multi-tenancy.
In a typical setup you will only need an instance (a virtual Zitadel system). This already supports B2C and B2B deployments.
If you want to host multiple customers, fully isolated, you could create an instance for each customer. However this is only necessary if you want to become a Zitadel service provider in most cases ;-)
Some docs for this:
Organization vs Instance: https://zitadel.com/blog/multi-tenancy-with-organizations Instance: https://zitadel.com/docs/concepts/structure/instance Organization: https://zitadel.com/docs/concepts/structure/organizations
Hope this helps!