PowerApps formula to save a record locally if device is offline, or submit it to datasource otherwise.

PowerApps_SubmitIfOnline_SaveIfOffline.txt

If(
    Connection.Connected,
    Patch(
        'My SharePoint list',
        Defaults('My SharePoint list'),
        {
            Title: Concatenate(
                "Leave Request - ",
                User().Email,
                " - ",
                Text(
                    Now(),
                    "[$-en-GB]dd/mm/yyyy hh:mm"
                )
            ),
            Requestor: currentUser,
            RequestorStaffNumber: txtRequestorStaffNumber.Text,
            LeaveRequestType: LeaveType
        }
    );
    Navigate(
        ConfirmationScreen,
        ScreenTransition.Fade
    ),
    ClearCollect(
        LocalRecord,
        {
            Title: Concatenate(
                "Leave Request - ",
                User().Email,
                " - ",
                Text(
                    Now(),
                    "[$-en-GB]dd/mm/yyyy hh:mm:ss"
                )
            ),
            Requestor: currentUser,
            RequestorStaffNumber: txtRequestorStaffNumber.Text,
            LeaveRequestType: LeaveType
        }
    );
    SaveData(LocalRecord, "LocalRecord");
    Navigate(
        PendingScreen,
        ScreenTransition.Fade
    )
)