Plex Documentation → Downloads for Offline Use → Downloads FAQ
See the table in the FAQ.
Unless both your Plex accounts were created before 01 Aug 2022, then your friend also needs a Plex Pass.
EDIT: As others have mentioned, if you invite a user into your Plex Home, then they can download media from your server without purchasing a Plex Pass. If you choose to do so, then you should PIN protect your account. Otherwise they can switch to your account via Fast User Switching. See Plex Home documentation for additional information.
