TFP401: 24-bit TFP401 to drive an 18-bit LCD panel, possible?
You want to use the TI chip or Adafruit board?

The board has a "40 pins TTL RGB" while your Sharp panel has a 51 pins connector.

It is also necessary to configure the decoder with the correct panel resolution as there is no automatic detection here.

18bits vs. 24bits isn't a problem, just don't use LSB bits.