var x = "x/y ( Hello 7)";
var y = new Regex("Hello 7", RegexOptions.Compiled | RegexOptions.IgnoreCase);
var result = y.Match(x);
Console.WriteLine(RuntimeInformation.FrameworkDescription);
Console.WriteLine($"{y}.Match({x}) = {result.Success}");
.NET 5.0.0-preview.8.20361.2
Hello 7.Match(x/y ( Hello 7)) = False