.NET 5 is here, and it's incredible! But... yes, there's a but. With all good things also come to some less good things. After all, it's impossible to make an omelet without breaking a few eggs, and .NET 5 is no exception. If you try to migrate from .NET Core 3.1 to .NET 5 you may run into a few breaking changes. Before jumping in with that migration and taking advantage of all the new features, make sure you have considered what may break first.

ASP.NET Core

Code Analysis

Core .NET libraries

Cryptography

Globalization

Interop

MSBuild

Networking

Serialization

Windows Forms

Windows Presentation Framework (WPF)

Also

For more details, you can take a look at the official documentation

Additionnal breaking changes regarding C# 9.0