Error when configuring PLL on STM32F767

>>Unfortunately I do not have the luxury of using any of the libraries.

Shouldn't prevent you from looking at the code and the logic, and understanding it in the context of the reference manual. These types of policies presume you can code better and more robustly than the authors of the other libraries. Have the people who defined the policy walk the code with you.

HSI is running the system at startup, no need to turn it on.

You need to have the PLL running BEFORE you select it as the primary clock source to the synchronous machine.

You need to select Flash wait states commensurate with the speed you are selecting. At least 5 for 192 MHz

Using 'RCC->PLLCFGR |=' 5+ times is very inefficient, write it once.

>>I have gone through the reference manual several times and can't identify the problem.

If you have to use this programming style you're going to need to get a lot better at this.