To restrict external viewers from changing date ranges in shared databoards, you can use the "Restrict date range change" setting inside the sharing settings of the dashboard.
Navigate to the Databoard and click on "Share".
Under "Additional Settings" click on "Restrict ability to view additional Date Ranges for external viewers".
This will ensure that the date range is restricted in the databoard public link.
Please note that any users invited to your Databox account will still be able to change the date range of the databoard.
Please note that while Databoards support the option to restrict the ability to change date ranges, this is currently not supported for Databoard Loops.