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Z390 A Pro not booting after SSD install

Level 7

I had installed a SSD this morning to use as expanded storage, but it wasn't showing up on my list of drives until I realized I had to enable m.2 in BIOS.

After enabling, the SATA mode switches from AHCI to RAID which then causes an Inaccessible_Boot_Device error when restarting.

I can't seem to set it to AHCI and save. Any time I exit BIOS it goes back to RAID.

I have a HDD as my boot drive and disabling m.2 allows the computer to boot normally with no error. How can I enable my m.2 without getting the boot error? I've only ever put together PC's with HDD's and this BIOS issue is a first for me.