Dynamic page title throws error

<?php

namespace App\Filament\Resources\TicketResource\Pages;

use App\Models\Ticket;
use Filament\Pages\Actions;
use Filament\Resources\Pages\ViewRecord;
use App\Filament\Resources\TicketResource;

class ViewTicket extends ViewRecord
{
    protected static string $resource = TicketResource::class;

    protected static string $view = 'filament.resources.tickets.pages.view-ticket';
    protected static ?string $title = 'Ticket n.' ;

    public function mount($record): void
    {
        $ticket = Ticket::find($record);
        $this->number = $ticket->number;

        // Imposta il titolo dinamicamente
        ViewTicket::$title = "Ticket n.{$this->number}";
    }

    protected function getActions(): array
    {
        return [
            //
        ];
    }
}