username is the current user that you are logged in with…
if not there there you would have configured a different location for .nuget folder…as that folder hosts all the packages you need
also what package feeds are present? you can check in in manage packages → settings
this is official feed if not present add it https://pkgs.dev.azure.com/uipath/Public.Feeds/_packaging/UiPath-Official/nuget/v3/index.json
cheers