This blog post also helps you if you are looking for How to Export CSV files from ASP.NET core? or How can I return a CSV file in ASP.Net Core? or How to create a web API that returns .csv file as output? or How to return .csv file from .NET Core controller?
What’s new in Microsoft .NET 5? Microsoft .NET 5 is the next release after .NET Core 3 and this is the big release in the .NET family.