error NU1100: Unable to resolve 'Microsoft.AspNetCore.SpaServices.Extensions
Solution 1:
Try installing the version 5.0.1, Link. I faced the same issue a while back and it was fixed by installing a lower version. If it doesn't work, then try installing version 4.8
Solution 2:
Oddly for my project, the user's computer couldn't find restorable packages because it didn't have a mapping for (the real) nuget. We had to add (or run from powershell):
dotnet nuget add source --name nuget.org https://api.nuget.org/v3/index.json
Then nuget restore worked and the error went away.