Hello @Mike,
Welcome to Microsoft Q&A forum.
Probably, you need to add another valid package source for VS to find the specific packages.
Please click Tools > NuGet Package Manager > Package Manager Settings > Package Sources > check if nuget.org
package source has been added. If it hasn’t been added, please click the “Add” button on top right corner > change the Name to nuget.org
and the Source to https://api.nuget.org/v3/index.json
> click Update > click OK, then rebuild your project.
If it has been added, please try to remove other invalid package sources. If this issue persists, please share us the screenshot about the package sources for further check.
Sincerely,
Tianyu
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