Save keeps the title
The Save button records a film or series in My List. It does not store the full video or its subtitles. A poster visible in your list is therefore not proof that you can watch the programme offline.
For an actual offline movie
Use a download feature provided by your chosen viewing service for that edition and device. Check available space, permitted audio tracks and any expiration. Open the downloaded copy before leaving your connection rather than waiting until the journey begins.
For a different browser
Use the My List backup tool to move saved catalogue choices. Its text contains title identifiers and checkpoints, not a movie file. It cannot transfer a service login or unlock another device's edition.
When searching for a video downloader
Decide whether you want a reminder, a list transfer or offline playback. The appropriate action is different in each case. An unrelated downloader or APK is not required to save a film recommendation here.
Before a long trip
Confirm that the downloaded edition is the correct year and has the language you need. Test playback in the service's supported offline mode. If no offline edition is available, leave the original title in My List and select another film for the journey.