.net core / standard string.ToLower() has no culture parameter

In .net fx i can do

myString.ToLower(frenchCulture);

But when looking at .net core or .net standard there is no more a culture parameter that can be passed. There is only string.ToLower() and string.ToLowerInvariant()

Should the culture just be ommitted ? But shouldn't then there be issues when the culture of the string is not the current culture?

Any hints what the reason behind this is?

When I have the idea of a invariant culture I can use ToLowerInvariant().

But what about use cases where i have to use string.ToLower() in a culture that is not the current culture?