EPPlus VS JourneymanToolkit

Like others, I recommend using the ImportExcel module. It uses and wraps EPPlus Software (EPPlus - Create advanced Excel spreadsheets using .NET (GitHub Project Old / New)) which is a DLL that is included with the ImportExcel PowerShell Module.

Their documentation looks okay. I doubt you're going to get many people familiar with a specific library here.

If you're copypasting stuff from excel, another approach I used in a different project is this package: https://github.com/EPPlusSoftware/EPPlus - which works in Blazor. You'd just let users drag/drop or upload their excel and import it, instead of copypasting

There is one Excel Library that I would recommend using in C# and that EPPlus. Its great and its free for non-commercial use. The API is simple to use and its got great documentation.

There is a Getting Started section in GitHub and complete API documentation on the home page

I've personally had a great experience working with EPPlus. It has both commercial and non-commercial/free licenses: https://epplussoftware.com/

Here is the link to the project I did with Epplus. it was a simple formatting tool so the code may not be in the best shape possible: https://github.com/MohamedA-Ibrahim/JourneymanToolkit/tree/main/RetakesFormatter