What to Expect When Switching to UEFI in MSI BIOS?

I totally get your concerns about the 'SATA Devices Support' option. When it goes to 'Last Boot HDD Only,' it's not disabling your SATA devices; it's just prioritizing the one that's set for boot. If you convert your OS drive to GPT and everything is done right, both your SSDs should remain functional—just ensure they’re recognized in UEFI settings.

When you switch to UEFI, your boot device needs special formatting, and you’re right about needing to convert to GPT. UEFI only shows drives that have boot loaders, so if your Windows was installed in legacy (CSM mode), it won't boot after you switch. It sounds like you’ll need to do some prep, like backing up your files and possibly reinstalling Windows. Also, the 'SATA Devices Support' changing means it’s focusing on the last boot device, which is common in UEFI setups, but as long as your SSDs are detected, you should be fine.

You're on the right track with the changes. UEFI gives you better management of boot devices compared to CSM, which lists all connected drives regardless of the OS. So, if you change to UEFI, and your Windows was installed under CSM with MBR, your system will likely not recognize the drive anymore. You’ll definitely want to convert your disk to GPT. Make sure you have a backup and a bootable USB for Windows just in case you need to reinstall.