

Two ways I like to get files to/from a mobile device: Syncthing (Möbius on iOS) or ResilioSync.
Resilio has a great feature, Selective Sync, that enables arbitrarily syncing files from a remote location. Nice for grabbing specific files when needed.
Unfortunately neither one handles any kind of reading status, they’re just file sync.
Others have mentioned SFF desktops.
My current server is an old Dell Optiplex SFF desktop. Idles at just under 20w, peaks at 80. Currently has an NVME boot drive, and an 8TB 3.5" drive.
Runs like a champ, easily serves Jellyfin video, with transcoding, while converting videos with handbrake (and with 2 other systems converting videos off that drive over the net).
Cost, internal space, options and power it’s hard to beat an SFF. If you don’t need internal space or conversion power, than a NUC can work (the lack of sufficient cooling limits it’s converting capabilities).