Iirc it uses webtorrent, which is a torrent protocol that runs in-browser for the most part.

Small file live on their servers using end-to-end encryption for the 24 hours.

Larger files are treated as a peer-to-peer torrent, which means that the tab needs to stay open until your downloadees are done grabbing it.

I’ve been using https://wormhole.app/ for file transfers over discord/text. The link is only good for 24 hours, but it supports up to 10 gb files.