I have a general flow question. I do not want to have a monolithic single project for all my ressources as it grows exponentially and the chance of breakage get higher. So for now I have split a lot of my ressources in separate projects. My question is how do I handle dependencies cross project. Let's say I have a project that takes care of keys or secrets generation. I want another project to be able to depend on that one in its flow. I can of course just use static resource names, but I'd of course prefer that it can somehow propose running through the secrets project.

You'd use Stack outputs and reference them in downstream projects. https://www.pulumi.com/learn/building-with-pulumi/stack-outputs/ https://www.pulumi.com/docs/using-pulumi/stack-outputs-and-references/

but how would I import the stack output of project1/ in project2/ ?

See the Using Stack References section: https://www.pulumi.com/docs/using-pulumi/stack-outputs-and-references/#using-stack-references

ahhhh I missed that somehow, thank you @adventurous-butcher-54166