@rednaxLamington Microsoft.WinForms.Utilities.Shared.dll is a design-time assembly. It is not available at runtime.
Microsoft.Winforms.Designer.Sdk NuGet package should be used with design-time assemblies only which means you will need to separate your design time code into a separate project, bundle it into a NuGet package, and then reference this NuGet package in your WinForms .NET application. More details about it are available in following wikis:
a. https://devblogs.microsoft.com/dotnet/custom-controls-for-winforms-out-of-process-designer/
b. https://learn.microsoft.com/en-us/dotnet/desktop/winforms/controls-design/designer-overview?view=netdesktop-9.0
c. https://github.com/microsoft/winforms-designer-extensibility/blob/main/docs/sdk/control-library-nuget-package-spec.md

I know it's a design-time assembly. I also tried to move the component to a winforms class library (which is always a good thing to do). But because of the transitive behavior of SDK projects, this design time assembly will also be included in the main project.

To be forced to create a package for your component is in my opinion way to complex, difficult to maintain and certainly not practical.

For now I found another way of dealing with this problem. When you create your controls in separate class library, you can block the transitive behavior with making the assets private:

  <ItemGroup>
	  <PackageReference Include="Microsoft.WinForms.Designer.SDK" Version="1.6.0" >
		  <PrivateAssets>all</PrivateAssets>
	  </PackageReference>
  </ItemGroup>

It's a dirty hack, but as long the Microsoft.WinForms.Designer.SDK package is not updated, this will work.

There will be an update to the Microsoft.WinFormsDesigner.SDK but unfortunately, I am unable to give a timeframe as yet. I'm glad you were able to find a workaround! For now, I will close this issue since you are not blocked. We will keep this in mind however for the next SDK update.