KDE Connect has been around for at least 5 years : https://apps.kde.org/kdeconnect/ . It is quiet amazing and does way more than only file transfert : clipboard sharing, multimedia control, ping, messages, remote keyboard/mouse, etc.
I also love KDE Connect; the clipboard sharing is so unobtrusive it feels almost magical. It takes less effort to copy and paste across my devices than it does between only Emacs and Vi on my desktop!
It seems to be not yet possible to share entire folders with KDE Connect, so I use Syncthing for that, which is also polished in its own, somewhat different way (more technical to use but optimised for large amounts of data).
KDE Connect expects you to mount the phone's directory to transfer folders, a decision I will never understand. You can use globbing to send every file in a folder though.
Airdrop is fast and works by physical proximity. You don't need to be in the same wifi, just near each other. That's what makes it so useful, otherwise I could just use a cloud solutions as I usually have internet access when I'm in a wifi.
>Both devices need to be on the same WiFi network or Hot Spot to be able to see each other.
It feels like very often when I see a Show HN project, the HN comments point out some critical missing feature.