Well, you could look for manga on platforms that offer offline download options. For example, some subscription-based services allow it. Just make sure you have enough storage space on your device and a stable internet connection for the initial download.
In most cases, it's not allowed. Crunchyroll is designed for online streaming to protect copyright and ensure a consistent user experience. Downloading for offline reading would violate their terms of service.
You might find offline manga reading options on dedicated e-readers like Kindle or Kobo. Some manga publishers also release digital editions that can be downloaded for offline viewing. Also, check if your local library has digital manga collections available for borrowing offline.