InDesign cloud documents are Adobe's cloud-native document file type that can be accessed online or offline directly from within the InDesign application. You can access these cloud documents across devices while your edits are automatically saved on the cloud.
Beta version can be installed directly from Creative Cloud (CCD) app, from Beta Apps section.
This is a geographically limited rollout. The InDesign Beta build is only available to users in the UK, US, Australia, and Canada at this time.
If you do not see the beta update in Beta Apps section in CCD app, go to Help>Check for Updates. If you are still not able to see the update, try logging out and logging back into Creative Cloud Desktop app.
You can use this forum to submit a bug or a feature request specifically for InDesign (Beta).