I spent a few days on the subject, here is my result :
https://www.grimoire-command.es/2021/artix_linux_on_raid_with_full_encryption.html
1.1. The objective
1.2. RAID
1.3. Full LUKS encryption
1.4. The grub-install problem on RAID
1.5. GRUB on RAID : Diskfilter writes are not supported
1.6. A last trap : a missing .img in /boot
Nice work. Thanks for sharing.