Pseudo code to show how to allocate an instance of a server on ESP8266 or ESP32.

allocateServer.ino

#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WebServer.h>
#include <ESP8266mDNS.h>

ESP8266WebServer *server;

void setup(){
  //This allocates a new instance of ESP8266WebServer
  server=new(ESP8266WebServer);
  if(server==NULL) //Insert code to handle allocation-error
  //Setup your server here
  server->begin();
}

servernolongerneeded(){
  //This destroys the allocated server and frees up all the resources it used
  delete(server);
}