Can't make builds since updating to 2021.1.6f1

Entity Component System (ECS)
1

Was using 2020.2.7f1. Updated to 2021.1.6f1. Can no longer make builds

ArgumentException: The Assembly System.Private.CoreLib is referenced by Unity.Entities (‘Library/PlayerScriptAssemblies/Unity.Entities.dll’). But the dll is not allowed to be included or could not be found.
UnityEditor.AssemblyHelper.AddReferencedAssembliesRecurse (System.String assemblyPath, System.Collections.Generic.List1[T] alreadyFoundAssemblies, System.String[ ] allAssemblyPaths, System.String[ ] foldersToSearch, System.Collections.Generic.Dictionary2[TKey,TValue] cache, UnityEditor.BuildTarget target) (at <9b8dec54b88e4aa9b9661a30f7e3f61e>:0)
UnityEditor.AssemblyHelper.AddReferencedAssembliesRecurse (System.String assemblyPath, System.Collections.Generic.List1[T] alreadyFoundAssemblies, System.String[ ] allAssemblyPaths, System.String[ ] foldersToSearch, System.Collections.Generic.Dictionary2[TKey,TValue] cache, UnityEditor.BuildTarget target) (at <9b8dec54b88e4aa9b9661a30f7e3f61e>:0)
UnityEditor.AssemblyHelper.FindAssembliesReferencedBy (System.String[ ] paths, System.String[ ] foldersToSearch, UnityEditor.BuildTarget target) (at <9b8dec54b88e4aa9b9661a30f7e3f61e>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)

7119643–849952–manifest.json.txt (2.16 KB)

2

I see Entities package in you manifest. You might want to consider downgrading to unity 2020 because of entities compatibility.

3

Thank you for the response.