Create a .NET DLL from a C# project
Applies to: 
SQL Server 2019 (15.x) and later versions
Learn how to package your C# code into a dynamic link library (DLL) file, when using SQL Server Language Extensions.
Create a .dll file
To create a .dll, navigate to the folder containing your C# project and run this command, where MyProject.csproj is the name of the project file:
dotnet publish MyProject.csproj