Was the STM32H7 2MB RAM? It seems that the STM32MP157 supports a lot of external memory.
The STM32MP157A/D devices incorporate high-speed embedded memories with 708 Kbytes of Internal SRAM (including 256 Kbytes of AXI SYSRAM, 3 banks of 128 Kbytes each of AHB SRAM, 64 Kbytes of AHB SRAM in backup domain and 4 Kbytes of SRAM in backup domain), as well as an extensive range of enhanced I/Os and peripherals connected to APB buses, AHB buses, a 32-bit multi-AHB bus matrix and a 64-bit multi layer AXI interconnect supporting internal and external memories access.
The STM32MP157A/D devices provide an external SDRAM interface supporting external memories up to 8-Gbit density (1 Gbyte), 16 or 32-bit LPDDR2/LPDDR3 or DDR3/DDR3L up to 533 MHz.
https://www.st.com/en/microcontrollers-microprocessors/stm32mp157a.html
Code should reside in SRAMs/RETRAM as Cortex-M4 performance execution penalty for running code from external memory will be extremely high (has there is no caches and bus paths are not optimized for that).
https://community.st.com/t5/stm32-mpu-products/stm32mp157-memory-for-the-m4-core/m-p/123138
