They see your charts, live and free. Viewers never need a license: every chart renders and updates for anyone who opens the workbook with the free Deltaline add-in available, and opening it never contacts the license server.
What they need is the free Deltaline add-in in their Excel. Either they add it themselves from Microsoft Marketplace, which costs nothing for viewing, or their IT admin deploys it for everyone (see Deploy Deltaline in Microsoft 365). Until the add-in is available to them, Excel shows an add-in message in the chart’s place instead of the chart. Once it is, the charts load and stay live for them, in Excel on Windows, Mac and the web.
A colleague without a license who clicks Edit on a Pro chart sees “Editing this chart needs a Deltaline license.” Export stays available to them. More in Share a workbook with charts.