Does the MCU rt1064 support booting from external SPI flash? Or does it only support booting from internal flash?
So clarify, the 1064 has the FlexSPI2 wired to internal flash, so it cannot be used to boot from external flash. Depending on your needs, you can write a program to the internal flash that will simply execute code from the external flash, which will look a lot like booting from external flash.
i.MXRT1064 supports FlexSPI2, SD and eMMS boot devices.