There is no more packages solution folder in any csproj or project.json-based .NET Core project.
NuGet CLI gets the list of us
From the MS docs:
global‑packages
Override using the NUGET_PACKAGES environment variable, the globalPackagesFolder or repositoryPath configuration settings (when using PackageReference and packages.config, respectively), or the RestorePackagesPath MSBuild property (MSBuild only). The environment variable takes precedence over the configuration setting.