.asmdef files and Libraries with DLL files only. Source editor doesn't see any Classes.

I’m trying to use .asmdef files in my project.
I put .asmdef files to all external libraries, but my source editor didn’t see any library classes from libraries with DLLs only (for example Firebase).

How to resolve this issue?

What do you mean by

I put .asmdef files to all external
libraries

assembly definition files control the compilation of source files into seperate assemblies. If you have already compiled libraries asmdef files are pointless. Also what is your “source editor”? If you imported a third party C# assembly into your project, Visual Studio should “see” the classes defined in those already compiled assemblies. Not the source of course, but the class members, signatures of the methods, etc.

What kind of DLLs do you actually import? If it’s a native code plugin (C++ / C library) you need some C# wrapping code. If it’s actually a C# assembly, just make sure you set up the dependencies / references for your own assemblies correctly. So if your classes which you put in a seperate assembly (by using an asmdef file) should have access to one of the third party assemblies, you have to put that third party assembly into the references of the asmdef file.

Just think of an asmdef file as a seperate C# project that only contains some of your files. It will be compiled seperately from everything else into its own assembly. Of course you have to specify which other assemblies you depend on.