Syncthing, Resilio Sync, or one of those browser based p2p file sends e.g. https://file.pizza or similar.
If both p2p ends know how to use torrents then creating a simple torrent to share to the other peer would work fine. But that requires slightly more IT competence especially if someone needs to open a port forward (ideally you would make sure you have your own port forwarded so the other party doesn't have to worry about this).
If you're doing this more than once it might be worth setting up a simple server e.g. HFS is a nice open source/free HTTP file server, been a while since I used it but it still seems to be active https://www.rejetto.com/hfs/