Visual Studio says "One or more projects in the solution were not loaded correctly."

I just switched to Unity Version 2020.3.30f1 and when I try to open C# file in visual studio, it gives a warning that the project wasn’t loading correctly.

The output says that these two files could not be found.
Unity.Mathematics.Editor.csproj
Unity.InternalAPIEditorBridge.001.csproj

Everything seems to still work however, it just give a message every time the .sln file is opened

Projects created with earlier versions also don’t even seem to have these files. When loading earlier versions it only has to load 1 project, while in the new version it has to load 35.

I’m just wondering why this is happening or how I can fix it. Thanks.

Not sure about your specific issue, but I’ve found the Visual Studio solution can get messed up from time to time.

If you close Visual studio, delete the SLN file in the root of your project folder (backup if you wish), then double click a script in Unity to return to visual studio that normally fixes issues with missing libraries, etc for me. (SLN file is regenerated automatically)