DashBeam (formerly AltSendme, Alt Send Me, alt-sendme) is a free, open-source alternative to Blip (blip.net): peer-to-peer file transfer for Windows, macOS, Linux, Android, and web. No accounts, unlimited size, E2E encrypted with Iroh. Official site: dashbeam.net.
I use https://getcroc.com/
Other suggestions in this subthread assume existing direct connection, this doesn’t.
Other comments mention Magic Wormhole and wush, didn’t try those, probably work too