If your rpi is a pico, then you can use it with meshtastic. https://meshtastic.org/docs/hardware/devices/raspberry-pi/

As for the pi boards that run Linux, as far as I can tell, the answer is that there's no software that implements the protocol Meshtastic uses. It could be written, or the existing code could be ported to a Linux executable, but I haven't seen anyone do that.