Simple serial communication techniqu

I want to intercommunicate data between daiy seed and raspberry pi pico.
Is there a simple way to implement this with serial communication?
For example, is there a mechanism to use pub/sub like MQTT?
Or I am thinking of sending json via UART.

Wouldn’t MQTT require networking? Daisy has no networking.

Async serial is easy, might be all you need.

Thank you very much.
I will adopt the method of sending json via UART.