And specifically this can be tested by a restart from the Windows side rather than a shutdown, which should actually release the hardware.

Ah, I see. Definitely possible to set up something like nextcloud or immich for file and photo backup. Then use a VPN like tailscale or wireguard to access while out of the house, or setting it up publicly available (usually being a reverse proxy).

Absolutely. Plenty of backup software will work with an external drive, provided it’s plugged in. Hell even a cron job would work.