exchange/app/Models/Multimedia.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Multimedia extends Model
{
    use \Backpack\CRUD\app\Models\Traits\CrudTrait;
    use HasFactory;

    protected $guarded = [''];

    public function multimediaCategory()
    {
        return $this->belongsTo(MultimediaCategory::class);
    }

    public function setMediaAttribute($value)
    {
        $attribute_name = "media";
        $disk = config('backpack.base.root_disk_name');
        $destination_path = "public/uploads/media";

        $this->uploadFileToDisk($value, $attribute_name, $disk, $destination_path, $fileName = null);

        // return $this->attributes[$attribute_name]; // uncomment if this is a translatable field

    }
}