Resolved! I need to use SPI without a clock, Cube MX won't let me do it.
It's a niche application. STM32H5 QFNI need SPI2_MOSI to make a specifically shaped wave. SPI is works well for this. I do not need the SPI_CLK pin/function. I set Cube MX to SPI2 Transmit Only Master, and of course it applies the CLK pin because alm...