moved project to new version of Unity, Weird stylehseet error

Questions & Answers
1

I moved the project from version 2020.1.15f1 to version 2021.1.7f1. Doing so caused these 3 errors to appear:

First:
Library\PackageCache\com.unity.ui.builder@0.10.1-preview\Editor\Utilities\Importers\BuilderStyleSheetImporter.cs(6,48): error CS0246: The type or namespace name 'StyleSheetImporterImpl' could not be found (are you missing a using directive or an assembly reference?)
Second:
Library\PackageCache\com.unity.ui.builder@0.10.1-preview\Editor\Utilities\Importers\BuilderStyleSheetImporter.cs(13,44): error CS0115: 'BuilderStyleSheetImporter.DeclareDependencyAndLoad(string)': no suitable method found to override
Third:
Library\PackageCache\com.unity.ui.builder@0.10.1-preview\Editor\Utilities\StyleSheetExtensions\StyleSheetUtilities.cs(13,25): error CS0246: The type or namespace name 'StyleSheetImporterImpl' could not be found (are you missing a using directive or an assembly reference?)

I tried deleating the folder so the project would automatically import updated files, but when it imported the files, they still have this error. Any clue?

2

found out why, removed UI Builder package to resolve, as it is experimental. Not sure if i ever even used it, but just in case does anyone know what the latest alternative to this is package?