Somehow USB disks are still the easiest and most reliable way

https://github.com/localsend/localsend

I used localsend on desktop, laptop and my phones to sync stuffs between OSes and phones. What I likes is that it support multiplatform out of the box and works flawlessly between Windows, Android and Linux distros (tried both on Ubuntu, and LM without problem). It's just SHAREit without any stupid weird stuffs on it.