netcore cause：error NU1100: Unable to resolve 'Swashbuckle.AspNetCore (>= 6.4.0)' for 'net8.0'.

What does the dotnet nuget list source command returns? If it's empty, it might be an issue with your NuGet sources.

You can try dotnet nuget add source https://api.nuget.org/v3/index.json -n nuget.org to fix if it's empty.