I have got brand new installation of VS2019 Community (release version) beside VS2017. When i load project to work on there is constantly about 30% of CPU is using on idle.
Project is completely loaded, analyzed and running on IIS Express. Project is small and running with no problems on VS2017 (C# + ASP.NET Core MVC)
I had the same problem as you today. Fresh Visual Studio 2019 installation and my CPU was constantly on around 30%. I noticed that Visual Studio is indexing files. On the left bottom corner you can click on an animated icon to see what is going on. After it finished this process my CPU went down to 1-2%.