Upgrading INpgsqlArrayConverter to PrimitiveCollection

[payoff]

I am in the process of upgrading a huge working project from Entity Framework Core 7 to version 8, which utilizes a significant number of INpgsqlArrayConverter instances to store various types of data in PostgreSQL arrays. We also make use of Jsonb, but we do not like the idea to migrate all of our existing data.

One of the converters we have been using is shown below:

public class DictionaryListStringsConverter : ValueConverter<Dictionary<string, List<string>?>?, List<string>?>, INpgsqlArrayConverter
{
    private static readonly KeyValueListStringsConverter _converter = new();

    public DictionaryListStringsConverter()
        : base(v => ToProvider(v), v => FromProvider(v)) {}

    public ValueConverter ElementConverter => _converter;

    private static List<string>? ToProvider(Dictionary<string, List<string>?>? dictionary)
    {
        return dictionary?.Select(x => _converter.ConvertToProvider(x)).Cast<string>().ToList();
    }

    private static Dictionary<string, List<string>?>? FromProvider(List<string>? list)
    {
        var dict = list?.Select(x => _converter.ConvertFromProvider(x)).Cast<KeyValuePair<string, List<string>?>>().ToList();
        return dict == null ? null : new Dictionary<string, List<string>?>(dict);
    }
}

Now the result code is something like:
repro code gist

However, when attempting to create a migration, we encounter the following error:

Unable to create a 'DbContext' of type 'TestContext'. The exception 'The 'Dictionary<string, List>' property 'TestEntity.AllowedTransitions' could not be mapped because the database provider does not support this type.

Personally, I find the old implementation far superior as it aligns seamlessly with the PostgreSQL way of working.
Any assistance or guidance would be greatly appreciated.

Regards,
Michele.