Hi Ryan,
The debugger hardware in Cortex-M devices does enable data breakpoints, when an address range is accessed. And IAR supports creating data breakpoints, like the screenshot below.
But if you are writing to external flash, you are using a driver, and the core may not see an access to that specific address in flash. Depends on how the flash is programmed/erased. In that case, your flash address is passed to the driver to do the programming. I would add a line of code in the driver to test the address, and see if it is in the range you are concerned about. Then add a code breakpoint at that line of code, so you halt whenever the app tries to write to that address.
Best regards
