SFM and Gmod versions probably use an mdl format that requires decompiling with Crowbar, which would generate an .smd file that requires Blender to have a plug-in to import.
The .blend you have is probably incompatible with your version of Blender. What version of blender was the .blend created in?
So that's a pretty old model, since 2.83 was released this year. I'm pretty sure that you're experiencing a compatibility issue.
I find it pretty strange that there's no .obj, .dae, nor .fbx variants, since those are very common model formats that can be used with multiple programs.