Thank you for clarifying this! Whilst I hear where you’re coming from, I am afraid at this time in order for users to be able to view data within the dashboard, they will need to have access to the private source (/those hidden tables)- this is simply to maintain the privacy and security of the data within those spaces.
Is this feature request similar to your idea? Having the ability to customise which data/columns users (outside of the private/shareable board) can access? Feel free to add your vote!
We also encourage you to submit a feature request specific to dashboards too 