I am looking for a way to back up my data to a pc at my parent's house. Is there a good solution for this?

Ideally it would be open source, run on linux, and I would prefer not to run an ftp server on my machine. I would like it to automatically download the files to their pc whenever there is an update to a certain drive/folders on my pc.

The solutions I have thought of so far were sftp, torrent, and cloud storage solutions. Ideally it would be peer-to-peer and I wouldn't have to have a ftp server running on my pc. And I don't think torrents are ideal for this but I could be wrong. There is something called BitTorrentSync but it limits the number of folders for free accounts.

Is there something that I'm missing that would work great for this?

Synology NAS
Folders Sync option

always using it to backup from Nas to Nas (direct)

read about it

go for the + version (more stable n faster)

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Kuwait Data Recovery - UNIX GTC
The only reason for time is so that everything doesn't happen at once. By: Albert Einstein

Paid version is US$39.99 per year.. for the exact thing you want.. really that is not a lot to say thank you to developers that provide you the exact thing you are looking for. With it comes support when you need it. I used to look for exclusively FOS software but come to realise there is merit to sometimes paying for things.