Depending on your scenarios and objectives, you can choose from two technologies to access and extend Excel: Office Add-ins and the Microsoft Graph REST API.
Extend Excel functionality with Office Add-ins
With Microsoft Graph, you can read and modify Excel workbooks that are stored in OneDrive, SharePoint, or other supported storage platforms. By issuing REST API requests to Microsoft Graph, your web or mobile application can access Excel objects. To learn more, see Working with Excel in Microsoft Graph.