Can I backup a dockerized mysql database just by copying the container's volume?

Question

I started a mysql docker conainer and I plan to do phisical backups of the database periodically, just by copying the /var/lib/mysql volume. I've binded the volume to a host's folder like so:

version: '2.1'
services:
  db:
    image: mysql:5.6
    restart: always
    volumes:
      - ./db/data:/var/lib/mysql
      - ./db/config:/etc/mysql/mysql.conf.d/
    environment:
      - MYSQL_ROOT_PASSWORD=${ROOT_PASSWORD}
      - MYSQL_DATABASE=db
      - MYSQL_USER=user
      - MYSQL_PASSWORD=${USER_PASSWORD}
    ports:
      - "3308:3306"

Of course, before starting to copy the volume the database must be in a read only mode:

FLUSH TABLES WITH READ LOCK;

After the copying is finished the read only mode must be turned off:

UNLOCK TABLES;

Is there any problem with that approach, as long as the database servers operate under Linux? I mean, if try to restore the database from a backup on a Linux system in future given my approach will it work?

My database is too big so restoring it through a logical backup (like generated with mysqldump) would take hours. I need a faster alternative.

In MYSQL's official documentation - dev.mysql.com/doc/refman/8.0/en/backup-methods.html they explain how to make a phisical backup. First FLUSH TABLES WITH READ LOCK and then copy the memory block with a snapshot tool. Copying and moving a docker's volume with the filesystem's tools like cp and rsync is similar to a snapshot, but yet not exactly the same. That's where my hesitation comes from.