As far as I’m aware there’s currently no way to setup drives in RAID without wiping both of them.
I also haven’t tried encrypting my home/boot drive but normally if I want to make a complete backup of a drive I use Clonezilla. It’s saved my bacon many time including recently copying a HDD that was in the process of dying on me.
It might be easiest to just backup your home directory and reinstall Nobara to the drives after you’d set them up in RAID.