Does Picaso display modules support RS485?

No. Picaso display modules do not directly support RS485.
However, you can use MOTG-RS485 to connect a Picaso display via RS485. This will require one of the COM ports and a GPIO pin.
When using a gen4-uLCD Picaso display. It is advisable to use gen4-MOTG-AC3. This allows easy connectivity with the MOTG-RS485 through Picaso's COM1.