iTunes library and flash drive

iOS/iPadOS doesn’t provide any facility to copy media downloaded from its Music and AppleTV to external media - these being a deliberate measure (DRM - Digital Rights Management) intended to prevent unauthorised copying of copyright-protected media.

Media downloaded from other sources, stored outside of Apple’s own media Apps, may have greater flexibility upon where it is stored. You should note, however, that you’ll need an appropriate third-party App to play this media content.

no, not the apple appletv and apple music app they only support media that was synced from a computer directly

you may be able to copy media to a flash drive and have other players like vlc or the likes access it though