ProTreo

void Main()
{
	var urls = new List<string>();
	urls.Add("https://mysite1.com/");
	urls.Add("https://mysite2.com/");
	urls.Add("https://mysite3.com/");
	urls.Add("https://mysite4.com/");
	urls.Add("https://mysite1.com/post/168755988566");
	urls.Add("https://mysite2.com/post/168755988566");
	urls.Add("https://mysite3.com/post/168755988566");
	urls.Add("https://mysite4.com/post/168755988566");
	
	var regexPattern = "\\/post\\/\\d*";
	var r = new Regex(regexPattern);
	
	var filteredUrls = urls.Select(x => x).Where(x => !r.IsMatch(x));
	
	foreach (var url in filteredUrls)
	{
		Console.WriteLine(url);
	}
}