Hello @ranulf ,
As you can see, both SIN (for Master LPSPI Instance) and SOUT (for Slave LPSPI instance) are not used in the schematic and not connected to anything. However, the MBDT SPI block does not allow you to set the "None" option on the pin, so the pin will be initialized for SPI, but not used when data is transferred. The data that might appear on that pin will be ignored. In the "original" SPI protocol, there is a net to send data from Master to Slave (MOSI) and another one to exchange data from Slave to Master(MISO). But on TPL there a special use-case. Let me explain.

In the above image, you can see how data is being transferred from S32K to an MC33771 via TPL, and reverse. Basically, MCU is going to use an entire SPI instance as MOSI, and another SPI instance as MISO. When S32K will send a frame on the TPL bus, it will send the frame via the MOSI and SCK1. The CS1 falling edge (Slave Select) will cause the "11" sequence on the bus. The frame will arrive at the selected MC33771 device, but also, the "11" sequence on the bus will select the S32K slave LPSI instance so the message will get to the S32K as a loopback message. Now, as you know, an SPI Slave cannot initialize a data transfer. So this is the reason why the second SPI instance is used by the S32K and configured as Slave. When the MC33771 sends a response to the S32K, the MC33771 start of frame "11" which will set the falling edge event on the CS2. This will notify the S32K SPI Slave configured instance that the MC33771 is sending a response. The data will arrive at the S32K on the second SPI instance, configured a MISO
We can simplify the UM11310 schematic by having a look at the MC33664 Typical application circuit. Basically, there is no MISO_0, because the MC33664 will not send anything back to the MCU when it wants to transfer data on the TPL bus. Same, for the RX: the MCU will not send any response to the MC33664.

So, both of the blocks drop down pins and the schematics are correct, but the usage of the TPL protocol has created this special use-case.
Hope this helps,
Marius