Hi,
what kind of board revision you have?
On rev.C LIN transceiver is connected to PTD6/PTD7 only.
On rev.D there could be more options but as per schematic, by default, it is connected to PTB0/PTB1 using zero Ohms resistors

So try to select PTB0/PTB1 in pin muxing component.
Also be sure board is using external 12V power supply so LIN transceiver is powered.
BR, Petr