The ISO download, therefore, is a recurring need—not a one-time event. Each time you update VirtualBox on the host, you should obtain the matching ISO and upgrade Guest Additions inside every existing VM. Neglecting this can cause the "mismatched version" warning, where features degrade or fail.
If you'd like to dive deeper into VM optimization, I can help you: Set up for easy file transfers Fix graphics lag or resolution issues Configure Network Settings for faster internet in your VM download guest additions virtualbox iso