What are the browsers supported by ASP.NET Core Blazor?

Blazor server-side supports almost all modern browsers out of the box except Microsoft’s Internet Explorer (IE 11), which needs Polyfills to be supported.

[_Layout.cshtml/_Host.cshtml]

//polyfills to be added for IE 

<script src="https://cdnjs.cloudflare.com/ajax/libs/core-js/2.6.5/core.min.js"></script> 
<script src="https://polyfill.io/v3/polyfill.min.js?features=fetch"></script> 

Blazor WebAssembly (client-side) supports all the modern browsers except the Internet Explorer.
Check this link for more information.