Starting with the release of Strategy ONE (March 2024), dossiers are also known as dashboards.
When importing an Excel file with multiple columns, as a dataset for a dossier, it is not possible to parse it because the horizontal slider is missing in Workstation 2021 Update 3-5, as shown below:

The issue has been addressed in Strategy 2021 Update 6. Upgrade to this version, as soon as available, to take advantage of the fix.