After each update of MacOS or Visual Studio any project I open throws this error and can't restore packages. It happens in Visual Studio for Mac, the latest version.
Screenshot of the package console
Once I had a similar issue when a vpm connection was active, after disabling it Visual Studio had no issues with packages. But this time I don't have any VPN enabled.
For those who is interested, I found a solution to this issue.
dotnet nuget locals --clear all