rag/app/Http/Resources/ChatResource.php

<?php

namespace App\Http\Resources;

use Illuminate\Http\Request;
use Illuminate\Http\Resources\Json\JsonResource;

class ChatResource extends JsonResource
{
    /**
     * Transform the resource into an array.
     *
     * @return array<string, mixed>
     */
    public function toArray(Request $request): array
    {
        $title = $this->title;
        if(!$title && $this->created_at->diffInMinutes(now()) > 5) {
            $title = 'Новый чат';
        }

        return array_merge(parent::toArray($request), [
            'title' => $title,
            'messages' => MessageResource::collection($this->whenLoaded('messages')),

            'created_at' => $this->created_at?->format('Y.m.d H:i:s'),
            'updated_at' => $this->updated_at?->format('Y.m.d H:i:s')
        ]);
    }
}