The SPI function and UART function are sharing the same hardware pins.
The only difference is the configuration of the mode.

SPI uses synchronous mode with clock support.

The interface provides a transparent channel, which can help you
directly to send/receive ASCI I (hex coding) data and it always uses
the full-duplex mode.

In the current scope picture, SPI  is used with 8-bits per frame

The structure of the transparent channel is the following:

More informations about you will find in the ATC guide.