The irony here is the F750 (the F7 valueline equivalent) has 64KB of FLASH, but the demo code it ships with consumes close of 192KB, so a bunch of the "dark" FLASH on die.
STM32H750 and STM32H743 have the same DEV_ID in MCUDBG. So they have the same die. Flash above the flash announced in Flash size register may have been invalidated by some fuse and is probably untested. If even ST ships STM32H750 with a demo bigger than the announced flash, probably no fuse invalidates the flash...
Не надо делать мне как лучше, оставьте мне как хорошо