Certainly!

I’ve never used this one, but it could also work for you.

There’s PairDrop might have what you need. It’s for transferring files rather than uploading and then downloading later. You could get creative with authentication. Maybe put files in an encrypted archive file.

When I build my NAS/server last year, I bought a used Dell Optiplex from 2013 on eBay for $50. I tossed in an old SSD I had laying around, and squeezed in 42 TB worth of HDD drives. I added a PCIE SATA expansion card, and a 10 gig network card for 60 bucks to improve performance.

The only real downsides of doing it this way are

• No realistic way of upgrading hardware
• Limited space for internal drives
• No hardware transcoding abilities out of the box
• More power consumption than buying something newer

I use Kopia to backup to Backblaze B2. I also use the Kopia UI since I can’t be bothered to figure out the cli for it. I have it running constantly in the background so it automatically takes care of everything.