From the Amazon QuickSight documentation:
You can only share analyses with users or groups who are in your Amazon QuickSight account.
The other question you link to refers to QuickSight templates. Templates allow you to store the visual configuration and data schema associated with a dashboard and then easily replicate the dashboard for different sets of users or different data, within or across accounts. To create a template, you would first have an analysis with visuals created in QuickSight then go through the process of creating one and sharing to another account.
For checking permissions, you can use the API actions like DescribeTemplatePermissions to see who the templates are being shared with & DescribeDataSetPermissions to see who has permissions to access the dataset. You can also log QuickSight operations with CloudTrail for additional governance https://docs.aws.amazon.com/quicksight/latest/user/logging-using-cloudtrail.html
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