I've been using sharedrop.io which also is open-source [1] and it works quite nice, I particularly like this one because I don't have to install any third-party app on any of the devices.

I think on mac Safari usually doesn't work as well as in Chrome, but I've been able to transfer from Windows to iOS, Windows to macOS and macOS to iOS without installing a thing.

[1] https://github.com/szimek/sharedrop