First of all that “indirect” contact is not a reliable source… the statement of limiting that Z690 with only 32Gb is also very doubtful in such modern chipset and DDR5…
It’s just my opinion and hard to believe this…but possible.
There’s a few users with similar situation like yours, with different brands and system models that have successfully cross flashed OEM with RETAIL bios, this usually requires an SPI programmer (99%), a few can be done with the Intel FPT tool from the ME FW 16 tools package (That you can try it…).
Regular tools for flashing, like the ones you tried and the ones you may will always fails due to several ids on bios code and implemented security measures in modern bios AMI Aptio V based and UEFI specs.
The Intel FPT tool needs access to all regions of the SPI bios content for reading write operations (MSI usually is unlocked) and this tool ignores ALL and writes whatever the data we told too, so right or wrong it always user fault when incorrect data is provided to the tool.
You can wait for other user pov.
Good luck.
EDIT:
Backup dumps can be made with AFUWIN or the Intel FPT tool.
No one is going to lose their time in such operation, as theres too much data to change in bios spread across various modules (AMITSE, FsRecovery, DsdtAsl, AcpiAtd…etc…)
The term cross flash here used is force to program the IC/SPI with another bios.
And i’m sorry, but by the contents of your post, you don’t have enough knowledge to advance in this area, not going to advance further details. we don’t like to see users with death systems, especially when it’s their main system and not a spare.
I’m sure you’ll understand this, besides being your own choice.
Final note: You can use the official MSI ME Firmware ver: ME_16.1.30.2330 update file on your system, this will not interfere with the Corsair OEM bios.