smart move. Here are your best bets:

Dedicated NAS Appliances (Configured for Local-Only)

These are user-friendly, but you must disable all internet and cloud features during setup.

Synology DiskStation: Easy to use (DSM operating system), great for file sharing and backups.

QNAP NAS: Similar to Synology, often with more powerful hardware.

DIY NAS (Maximum Control & Privacy)

This gives you the most control and is truly local-first.

TrueNAS SCALE: My top pick. It's built on ZFS for superior data integrity and lets you run apps like Plex locally via Docker. Requires a bit more technical know-how and decent hardware.

OpenMediaVault (OMV): Lighter-weight, good for basic needs, and runs on less powerful hardware.

Unraid: Flexible with mixed-size drives and good for media servers (paid license).

Remember to physically secure your NAS and use router firewall rules to block any unwanted outbound connections for true isolation.