Loading .slnf files

I have this project structure

└── src
   ├── MRX.Core
   │   ├── MRX.Core.slnf
   │   └── src
   │       ├── bin
   │       ├── IServiceCollectionExtensions.cs
   │       ├── ModelBinding
   │       ├── MrxConfigurationOptions.cs
   │       ├── MRX.Core.csproj
   │       └── obj
   └── MRX.slnx
 

Where MRX.sln is

<Solution>
 <Folder Name="/src/MRX.Core/">
   <Project Path="MRX.Core/src/MRX.Core.csproj" />
 </Folder>
</Solution>

and MRX.Core.slnf is

{
 "solution": {
   "path": "../MRX.slnx",
   "projects": [
     "MRX.Core/src/MRX.Core.csproj"
   ]
 }
}

When I open the .slnf file directly Rider does not load the specific project only. It opens a window with Explorer in “File system” mode, when I switch it to “Solution” it displays the whole .slnx with all other projects.

Is this expected behavior, am I doing something wrong or is opening only projects listed in .slnf files not supported?