You seem to already know what you are doing and have experience with Spring Boot. I'm not sure if you're looking into also developing web applications for .NET, but have a look at the official ASP.NET Core documentation. There's a whole lot to be found there, and examples on how to develop different types of applications. Go through one or more you are already familiar with, and you'll find the .NET ecosystem and the C# language really isn't that much different from Java. The language itself shares most of its paradigms with Java, and even syntactically it is very similar.
You seem to already know what you are doing and have experience with Spring Boot. I'm not sure if you're looking into also developing web applications for .NET, but have a look at the official ASP.NET Core documentation. There's a whole lot to be found there, and examples on how to develop different types of applications. Go through one or more you are already familiar with, and you'll find the .NET ecosystem and the C# language really isn't that much different from Java. The language itself shares most of its paradigms with Java, and even syntactically it is very similar.