I tried creating my own torrent and was able to dl it on another device, but on her machine it stayed at 0% and wouldn’t let me connect to seed

At least one of the torrent clients needs to be fully connectable (port forwarded) for torrents to transfer data. You need to test that e.g. test your torrent client's incoming connection port with a port test website like https://www.canyouseeme.org, https://www.yougetsignal.com/tools/open-ports, etc. & make sure those port test websites can successfully test connect to your torrent client's incoming connection port. If the test fails then you need to look at opening the port via your OS firewall and/or router firewall.

Is FTP a good option? I set up a proxmox server last night but I don’t really know what I’m doing yet

Probably best to avoid FTP if you don't know what you're doing, it's not all that secure.. you'd want to at least configure SFTP or FTPS which is just going to be more complicated vs fixing your torrent issues. And technically you still need to make those connectable (port forwarded) too, just like your torrent client.

All that aside it's probably easier to use Syncthing if you can't get the torrent working.

You could also try one of those file transfer websites that use WebRTC to transfer data peer to peer e.g. https://file.pizza or similar. Not sure how well they work for huge amounts of data but their github page mentions that Firefox is better for that, apparently Chrome starts to choke with data 500+ MB.