ProGet does not support wildcard package references and search requests while the official NuGet servers do.
For example, to use the latest version, Micosoft suggests to use Wildcard references like:

<PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="7.0.0-*" />.

When using this, NuGet causes the following error message when trying to download NuGet packages:

NU1301: Failed to retrieve information about 'Microsoft.EntityFrameworkCore.Relational' from remote source 'https://nuget.intern/nuget/default/FindPackagesById()?id='Microsoft.EntityFrameworkCore.Relational'&semVerLevel=2.0.0'.