Which boards are compatible with Sx1280 transmitter?
what do you mean with that? The Sx1280 is chip what communicate over SPI or UART so you can connect it to any board what have a SPI or UART interface (which is standard for all, I think).
If you mean whole solution, then
- It seems the Mbed not support Sx1280 yet - connectivity/drivers/lora - GitHub
- You can also visit Semtech | Mbed there are some drivers directly form Semtech.