Is liscense key required to enable SSO on self hosted growthbook?

yes. SSO requires an enterprise license key

For integrating with Azure AD, will I have to register as application or Enterprise? As the steps suggest application. But they key reuires Enterprise

Yes, it's considered an "application" in Azure AD since we use OpenID Connect as the protocol

from where I can get the license key?

You can get a trial license key from within the app (there should be a Try button in the bottom left by the build number). That trial will last for 2 weeks. Beyond that, you can schedule some time with our sales team at https://www.growthbook.io/meet