A subscriber cannot view the code of components included in managed packages and most of elements included in a managed package are protected (the may also be IP protected).
Reference
Component Can be Updated During Package Upgrade:
- If no: The component can’t be updated during package upgrades. Instead, it’s only deployed to the subscriber org during the initial package installation, and subsequent package upgrades don’t update the component. Components in this category, can typically be modified by the admin in the subscriber org.
Component Has IP Protection:
- If yes: To protect the intellectual property of the developer, the component’s metadata, such as Apex code or Custom Metadata record information, is hidden in the installed org.
If you look at Lightning Component you'll find
- Component Is Updated During Package Upgrade - Yes
Therefore Aura Component and LWC included in a managed package cannot be retrieved from a subscriber org.
The same goes for Apex Class, Trigger, Flow, etc...
Going through the linked page you can know what you're able to retrieve (and modifify) and what is protected.