In the RM0399, Rev 4, June 2023 Reference Manual, it is still NOT clearly indicated that you can not decrease the ST_RAM_SIZE once it has been increased.
In CubeMX 6.12.0 for STM32H755BITx, I can not select DAC1_OUT2 to be monitored by ADC IN17. IN17 is not available for section - CubeMX skips from IN16 to IN18.