NuGet package name is DocumentFormat.OpenXml. Let’s install this package.
// Read and Create/Write Excel file in C# .NET Core https://www.thecodebuzz.com/read-excel-file-in-dotnet-core-2-1/
// Read Excel as JSON using Open XML SDK https://www.thecodebuzz.com/read-excel-as-json-using-open-xml-sdk/