It's unfortunately not FOSS, but I quite like https://wormhole.app/ - It's client side encrypted and P2P when possible
Now that we’ve shifted our company’s focus to https://socket.dev, I’d love to open source Wormhole. I’m quite proud of the code - I’ve worked on P2P and file transfer systems for so so long that I think this might be some of the best code I’ve worked on.
It’s just a matter of finding the time, but I expect this will be open source eventually.