Question: How do you resolve the error "MSBUILD : error MSB1011: Specify which project or solution file to use because this folder contains more than one project or solution file."
Login to See the Rest of the Answer
Answer: if you have just upgraded Visual Studio to the latest build, and then running dotnet watch run, this error shows up.
To resolve this, delete the ProjectName.sln file. There is a chance the SLN file name is different from the Solution Name.
If the above cannot resolve the issue, do not use "watch" when running dotnet, simply type "dotnet run".