NuGet should treat the values from TargetFramework and TargetFrameworks as aliases.

When setting the property TargetFramework=(alias) the actual target framework value can be evaluated from TargetFrameworkIdentifier and TargetFrameworkVersion.

See for examples and more details: dotnet/project-system#1938

Update by @nkolev92

NuGet in 5.8 and .NET 5.0 SDK now treats TargetFramework as an alias, however duplicate framework entries are not supported yet (ex. You can't target .NETCoreApp,Version=3.0 twice.)