OpenCVSharp4がインストールできません

Question

前提・実現したいこと

OpenCVSharp4をインストールしたい

発生している問題・エラーメッセージ

Nugetを使ってOpenCVSharp4をインストールしようとすると下記のエラーが出ます。

Could not find System.Numerics.Vectors [4.4.0, ) or greater.
UnityEngine.Debug:LogErrorFormat (string,object[])
NugetForUnity.NugetHelper:InstallIdentifier (NugetForUnity.NugetPackageIdentifier,bool)
NugetForUnity.NugetHelper:Install (NugetForUnity.NugetPackage,bool)
NugetForUnity.NugetHelper:InstallIdentifier (NugetForUnity.NugetPackageIdentifier,bool)
NugetForUnity.NugetHelper:Install (NugetForUnity.NugetPackage,bool)
NugetForUnity.NugetHelper:InstallIdentifier (NugetForUnity.NugetPackageIdentifier,bool)
NugetForUnity.NugetWindow:DrawPackage (NugetForUnity.NugetPackage,UnityEngine.GUIStyle,UnityEngine.GUIStyle)
NugetForUnity.NugetWindow:DrawPackages (System.Collections.Generic.List`1<NugetForUnity.NugetPackage>)
NugetForUnity.NugetWindow:DrawOnline ()
NugetForUnity.NugetWindow:OnGUI ()
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)

試したこと

System.Numerics.Vectorsをインストールしようとしましたがインストール出来ません。
上記と全く同じエラーが出ます。

補足情報（FW/ツールのバージョンなど）

Unity2020.3.2ｆ1

###追記

Nugetを使わず手動でダウンロードしたものを\Asset\Packagesに入れてみたところ

PrecompiledAssemblyException: Multiple precompiled assemblies with the same name System.Numerics.Vectors.dll included or the current platform. Only one assembly with the same name is allowed per platform.
UnityEditor.Scripting.ScriptCompilation.PrecompiledAssemblyProvider.ValidateAndGetNameToPrecompiledAssembly (UnityEditor.Scripting.ScriptCompilation.PrecompiledAssembly[] precompiledAssemblies) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.Scripting.ScriptCompilation.PrecompiledAssemblyProvider.GetPrecompiledAssembliesDictionary (System.Boolean isEditor, UnityEditor.BuildTargetGroup buildTargetGroup, UnityEditor.BuildTarget buildTarget) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.Scripting.ScriptCompilation.EditorCompilation.GetPrecompiledAssembliesDictionaryWithSetupErrorsTracking (System.Boolean isEditor, UnityEditor.BuildTargetGroup buildTargetGroup, UnityEditor.BuildTarget buildTarget) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.Scripting.ScriptCompilation.EditorCompilation.GetAllScriptAssemblies (UnityEditor.Scripting.ScriptCompilation.EditorScriptCompilationOptions options, System.String[] defines) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.Compilation.CompilationPipeline.GetEditorAssemblies (UnityEditor.Scripting.ScriptCompilation.EditorCompilation editorCompilation, UnityEditor.Scripting.ScriptCompilation.EditorScriptCompilationOptions additionalOptions, System.String[] defines) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.Compilation.CompilationPipeline.GetAssemblies (UnityEditor.Scripting.ScriptCompilation.EditorCompilation editorCompilation, UnityEditor.Compilation.AssembliesType assembliesType) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.Compilation.CompilationPipeline.GetAssemblies (UnityEditor.Compilation.AssembliesType assembliesType) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.Compilation.CompilationPipeline.GetAssemblies () (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
Microsoft.Unity.VisualStudio.Editor.AssemblyNameProvider+<GetAssemblies>d__9.MoveNext () (at Library/PackageCache/com.unity.ide.visualstudio@2.0.7/Editor/ProjectGeneration/AssemblyNameProvider.cs:58)
System.Collections.Generic.List1[T]..ctor (System.Collections.Generic.IEnumerable1[T] collection) (at <eae584ce26bc40229c1b1aa476bfa589>:0)
System.Linq.Enumerable.ToList[TSource] (System.Collections.Generic.IEnumerable1[T] source) (at <351e49e2a5bf4fd6beabb458ce2255f3>:0) Microsoft.Unity.VisualStudio.Editor.ProjectGeneration.GenerateAndWriteSolutionAndProjects () (at Library/PackageCache/com.unity.ide.visualstudio@2.0.7/Editor/ProjectGeneration/ProjectGeneration.cs:250) Microsoft.Unity.VisualStudio.Editor.ProjectGeneration.Sync () (at Library/PackageCache/com.unity.ide.visualstudio@2.0.7/Editor/ProjectGeneration/ProjectGeneration.cs:168) Microsoft.Unity.VisualStudio.Editor.ProjectGeneration.SyncIfNeeded (System.Collections.Generic.IEnumerable1[T] affectedFiles, System.Collections.Generic.IEnumerable`1[T] reimportedFiles) (at Library/PackageCache/com.unity.ide.visualstudio@2.0.7/Editor/ProjectGeneration/ProjectGeneration.cs:114)
Microsoft.Unity.VisualStudio.Editor.VisualStudioEditor.SyncIfNeeded (System.String[] addedFiles, System.String[] deletedFiles, System.String[] movedFiles, System.String[] movedFromFiles, System.String[] importedFiles) (at Library/PackageCache/com.unity.ide.visualstudio@2.0.7/Editor/VisualStudioEditor.cs:145)
UnityEditor.CodeEditorProjectSync.PostprocessSyncProject (System.String[] importedAssets, System.String[] addedAssets, System.String[] deletedAssets, System.String[] movedAssets, System.String[] movedFromAssetPaths) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)
UnityEditor.AssetPostprocessingInternal.PostprocessAllAssets (System.String[] importedAssets, System.String[] addedAssets, System.String[] deletedAssets, System.String[] movedAssets, System.String[] movedFromPathAssets) (at <d6a6a4b561b9431dbfe2c61f7bf0d405>:0)

というエラーメッセージが出ました。
System.Numerics.Vectorsが見つからないからOpenCVSharp4がインストールできず
System.Numerics.Vectorsは既に存在するからSystem.Numerics.Vectorsがインストールできない・・・
一体どういうことなのでしょうか？