If you installed Manjaro and you have no Windows, that means you already switched to AHCI from BIOS Settings, otherwise you could have not been able to do the install.
For the Nvidia part, reason why is booting to black screen or not booting with newer kernels you could try to add ibt=off to the grub kernel boot parameter. See this Lenovo Legion 5i 2021 boots to black screen after installing NVIDIA
Edit /etc/default/grub and add after quiet the ibt=off and save the file, then run from terminal:
sudo update-grub
Reboot the system in newer kernel. If it fails, boot back to the 5.15 one and try to get some logs.