variable decimal places in .Net string formatters?

Question

Fixed decimal places is easy

String.Format(\"{0:F1}\", 654.321);

gives

654.3

How do I feed the number of

Answer 1

I used two interpolated strings (a variant of Michael's answer):

double temperatureValue = 23.456;
int numberOfDecimalPlaces = 2;

string temperature = $"{temperatureValue.ToString($"F{numberOfDecimalPlaces}")} \u00B0C";