Which framework will support for next 20 years?

can you describe the difference between Blazor vs Razor.

Blazor is an SPA framework (runs in the browser) within the ASP.NET Core family of web frameworks. Razor is a markup language for rendering HTML. Razor Pages is a server side web framework in ASP.NET Core if that's what you mean by Razor.

Which one is better for long term enterprise level application?

Your question makes incorrect assumptions. The official documentation covers the basics.

Introduction to ASP.NET Web Programming Using the Razor Syntax (C#)

ASP.NET Core Blazor

How long Blazor will support?

No one can accurately answer this question.

what the future of Blazor for enterprise level projects?

This question is far to vague to answer. Again, Blazor is an SPA that runs in the browser. An enterprise application is made of many more parts than an SPA application. However, ASP.NET Core has everything needed to build an enterprise application.

Please mentions anything with good reference.

Your questions is feels like you recently started researching. I recommended going through the ASP.NET Core fundamentals which illustrates the different tools the framework has to offer.

Overview of ASP.NET Core

First Razor is a template language used by asp.net core. There are currently three uses:

1. MVC razor views. The Razor language is used to define MVC view file
2. Razor Pages. Razor page files define a webpage using the Razor syntax
3. Blazor razor compoenents. The razor syntax is used to define a Blazor UI components.

Twenty years is too far out. Will browsers still exist? Will webpages still be the standard UI?

Also, like many modern frameworks, asp.net core requires the enterprise customer to stay current. A LTS release is supported for 3 years. Before the 3 years are up, the code must be migrated to the next LTS release (typically you will have a year to migrate).. Breaking changes are allowed between LTS releases.

If you are asking for a web development framework to last 20 years you are doing something drastically wrong unless it's an intranet website. The architecture drift of the security updates that are going to happen as well as tooling changes will introduce more and more issues as your application ages. You should be planning a re-platform probably every 7 to 10 years or even 3 to 5 years for publicly accessible websites.