Check for fixed IP local server, and if not found, connect to default online photon settings.

LocalOrOnlinePhotonConnect.cs

using System.Collections;
using System.Collections.Generic;
using Photon.Pun;
using Photon.Realtime;
using UnityEngine;

public class LocalOrOnlinePhotonConnect : MonoBehaviour, IConnectionCallbacks
{
    [SerializeField] ServerSettings photonOnlineSettings;
    [SerializeField] Photon.Realtime.AppSettings photonOfflineSettings;


    void Start()
    {
        StartCoroutine(ConnectCheckForLocalServer());
    }

    IEnumerator ConnectCheckForLocalServer()
    {
        PhotonNetwork.AddCallbackTarget( this );
        var ping = new Ping(photonOfflineSettings.Server);
        float timeout = 1f;
        while(!ping.isDone && timeout>0){
            yield return null;
            timeout-=Time.unscaledDeltaTime;

        }
        Debug.Log($"isDone {ping.isDone} time={ping.time}");
        //PhotonNetwork.ConnectToMaster();
        PhotonNetwork.ConnectUsingSettings(ping.isDone ? photonOfflineSettings : photonOnlineSettings.AppSettings);

    }
    
    public void OnConnected()
    {
        Debug.Log("Connect To Server");
    }

    public void OnConnectedToMaster()
    {
        Debug.Log("On Connected To Master");
    }

    public void OnCustomAuthenticationFailed(string debugMessage)
    {
        Debug.Log($"OnCustomAuthenticationFailed {debugMessage}");
    }

    public void OnCustomAuthenticationResponse(Dictionary<string, object> data)
    {
    }

    public void OnDisconnected(DisconnectCause cause)
    {
        Debug.Log($"OnDisconnected {cause}");
    }

    public void OnRegionListReceived(RegionHandler regionHandler)
    {
        Debug.Log($"OnRegionListReceived {regionHandler.BestRegion}");
    }
}