Short answer
A free account can save one opportunity. To save another opportunity on the free plan, remove the existing one or upgrade.
How it works in Koreograph
You can start analysis before login, but saving requires authentication. The save point should guide you to login or signup and then continue the workflow once authenticated.
Developer view
Use the free account to test the full workflow on a real deal. If you are actively sourcing or comparing a pipeline, upgrading avoids losing the context between multiple opportunities.