In the solution explorer, you can group projects inside of solution folders to improve the manageability of solutions that contain a large number of projects.
With focus on the Solution node in the solution explorer, you’ll notice the Add New Solution Folder button become visible. Now you can drag and drop projects into this solution folder to hide, as shown below.
But let’s actually hide the project. Right-click on your newly created Solution Folder and click on Hide. Now the project is hidden, and new icon appears to unhide projects. (and yes, you can still build successfully in this state)