I am currently using Telerik Reporting version 15.1.21.616 (R2 2021 SP1) in my ASP.NET application. I noticed that the report viewer only exports to the legacy Excel format (.XLS) and there is no option for Excel (.XLSX) in the export formats.
I have checked the Bin
directory of my installation, and I do not see the Telerik.Reporting.XlsxRendering.dll
assembly, which I understand is required for XLSX export.