I'm getting an error when upgrading my Umbraco version. I'm not very experienced with .NET core, nuget and upgrading, but I'm pretty sure I ran an upgrade a couple of months ago that worked, but might have been on a different machine.

When running dotnet build it starts to run like this:

  Determining projects to restore...
  All projects are up-to-date for restore.
  Copying Umbraco content files: C:\Users\Administrator\.nuget\packages\umbraco.cms.staticassets\9.5.0\buildTransitive\..\content\umbraco\**\*.* - #47 files
  Copying Umbraco wwwroot content files: C:\Users\Administrator\.nuget\packages\umbraco.cms.staticassets\9.5.0\buildTransitive\..\content\wwwroot\umbraco\**\*.* - #2513 files

But then lists hundreds of errors like this...

C:\Websites\Project\appname\publish\umbraco\Data\TEMP\InMemoryAuto\models.generated.cs(19,11): error CS0579: Duplicate 'ModelsBuilderAssembly' attribute [C:\Websites\Project\appname\appname.csproj]

and also errors like this...

C:\Websites\Project\appname\publish\umbraco\Data\TEMP\InMemoryAuto\models.generated.cs(703,23): error CS0102: The type 'UmbracoMediaAudio' already contains a definition for 'UmbracoBytes' [C:\Websites\Project\appname\appname.csproj]

These are the steps I'm following to do the upgrade:

dotnet add package Umbraco.Cms
dotnet add package Umbraco.Cms.Core
dotnet add package Umbraco.Cms.SqlCe
dotnet restore
dotnet build

If anybody has any ideas that might help me then that would be great, as I can't find much information about this error on the web.