We have multiple .NET 6 apps and background workers which are hosted on Azure Container apps.
These are built on .NET 6.0 today.
Is it possible to use Aspire to orchestrate them?
The orchestration project is special. The target framework of the orchestration project does not affect what it can orchestrate. This means you can launch a .NET 6/7/8 application. As others have said, to get the full set of aspire features it requires .NET 8+. The Aspire.* packages depend on .NET 8 features to get the full end to end experience working including telemetry, resilience etc.
Upgrading from .NET 6 to 8 should be straightforward.