Best practices for shipping NuGet packages with global usings inside package-specific MSBuild file?

Some context: working on distributing a new version of our core NuGet packages that has some breaking changes which can be resolved by just referencing a namespace that has been available for years.

I'm interested in shipping a {package-name}.props file inside our NuGet package which will automatically apply the following:

<Project><ItemGroup Condition="'$(ImplicitUsings)' == 'true'"><PackageReference Include="MyProject" Version="6.1.0" /><Using Include="MyProject.NonDefaultNamespace" /></ItemGroup></Project>

Here is what I don't know how to do:

1. What's the right condition to apply here if I want to apply this global using statement to the largest possible number of legacy users? Check if ImplicitUsings is enabled? A .NET version? A C# language version?
2. Do I need to include a PackageReference to the package inside the ItemGroup or is that already done via the package being referenced inside the .csproj / .fsproj
3. Is this going to be a footgun in other ways I don't know about?

Thanks!