[Feature] Mobile App Option to Pre-Cache/Sync Entire Library Thumbnails for Offline Browsing

[removepardon-ui]

I have searched the existing feature requests, both open and closed, to make sure this is not a duplicate request.

• Yes

The feature

I would love to see an option within the mobile app settings to actively pre-cache or sync the entire library's thumbnails to the local device. Ideally, this feature would include:
1.a "Sync All Thumbnails" toggle/button that downloads the small timeline thumbnails to the phone's local storage in the background while connected to the home network.
1.b cache size/quality optimizer slider allowing users to choose the compression level of the local cache (e.g., 25%, 50%, or 100% quality) to balance offline visibility with phone storage limits.

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Currently, the Immich mobile app uses an on-demand (lazy loading) caching strategy. Thumbnails are only saved to local device storage if the user physically scrolls past them while connected to the server. If I travel offline or lose server connectivity (e.g., traveling without a VPN setup like Tailscale), any part of the timeline that wasn't previously scrolled through only shows blurry ThumbHash placeholders or blank boxes. Manually scrolling through a 100GB+ library to force a local cache before a trip is highly impractical.

Platform

• Server
• Web
• Mobile

[github-actions[bot]]

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