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Pretty sure it's IP based, but I haven't really looked.

KDE Connect is LAN/WLAN-based only. I have good experiences (no connection issues that I remember) using it between KDE and Android, and some trouble between Android phones, but last time I tried it would crash on Windows when I slept the computer.

Does it not work with a ad hoc wireless network? That seems perfect for situations without a wireless router.

Yes it does, I've done it in trains. Either by sharing the computer's wifi to the phone or the phone's wifi to the computer. It also works with when sharing the phone's connection via USB.

It should work if you manage to share a network connection through Bluetooth between the devices.

IIRC there is a bluetooth build for Android since a few years ago. Too buggy/beta though.