Hi there. Is it possible to create two different projects with different urls on ubuntu server? For example, flows running at localhost:8081 will not be visible at localhost:8080.

You would need two separate server instances for that. Server only has 1 default tenant. For Prefect Cloud, you would have multiple tenants.

Do I have to use the Cloud? I want to do this in prefect core, is it possible?

Project is not a core only thing. It’s part of the backend Cloud or Server. But Cloud has 20k free task runs every month so it’s a lot easier to get started with