I can't really help much, mostly because in my limited experience I have not had to mess with that since the XP/7 era. Can you not just set the bios settings you want, and then install your OSs and just have it work? Dual booting has always been relatively straightforward when I have done it. What OSes versions are you using and what hardware?
From past experiences, windows will only work with the mode that it was originally installed with, so if it wasn't installed with AHCI enabled before and you want it to use now you will need to re-install windows with AHCI enabled in your bios already.
The Ubuntu guide (https://help.ubuntu.com/rst ) and comments on stackexchange claim its possible, maybe it wasnt in the past. It hasnt worked for me, Ive given up and am going to reinstall windows like you suggested.
So you're in software RAID mode, basically you have two or more disks and Intel's software was faking a single combined disk? That one is a complete mess and is very unstable, I'd recommend switching it off.
There is a single hard disk but my computer comes with Intel optane, which seems to need RST. It has worked fine so far, maybe because of it not being multiple actual disks.
I don't have a Windows dual-boot anymore, but maybe try to boot from a Windows 10 live USB and see if the installer can repair it? If you're lucky it might notice that other hard disk drivers are necessary and will install them.
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