STM32 PWM output frequency is off
You cannot produce 12.288 MHz by integer division of a 180 MHz source.

The closest you would come would be dividing by 14, which would yield the 12.857 and some following decimals, which is likely within measurement error of what you think you got.

Perhaps you can adjust your goal to use that.  Or perhaps you can change the source crystal frequency to something which when multiplied up by the STM32 PLL and divided down will produce your goal more exactly.  There are yet more complicated ways of doing this - fractional N synthesizer, etc.

In the end solutions for turning one frequency into another have various power, cost, accuracy and phase noise consequences.  To pick one, you'll need to consider your specific requirements in detail.