What are good file transfer apps that can be used in similar scenarios? (to be clear about the usage model: communications on a plane)

* I see LocalSend and LANDrop frequently suggested on HN but in my experience they rely on having a central Wifi router. No good.

* Android's QuickShare comes included by default, but it's buggy. Just yesterday it failed on me (I'm on an uncommunicated boat): it was defaulting to Bluetooth, so I had to reboot both phones to finally make it work over Wifi Direct. Not to speak about the "oh damn, you have an iPhone" scenario. Not ideal.

Anything else? (to remark: for airplane-like situations so no access to Internet and no central router)

Unfortunately most P2P wireless solutions are likely to be somewhat buggy, at least in my experience. WiFi and Bluetooth chipsets are often "quirky". I will often lose the ability to ssh into my laptop across WiFi until I go to the laptop and poke the network from it. KDEConnect often temporarily loses sight of my phone, yet it still reports being connected to WiFi. Stuff like that.