raspistill is not available on arch64.
You have to install libcamera-git from AUR (disable check part) and compiles libcamera-apps as described on this site :
https://www.raspberrypi.com/documentation/accessories/camera.html#building-libcamera-appsOn the /boot/config.txt you have to add:
$this->bbcode_second_pass_code('', '#Automatically load overlays for detected cameras
camera_auto_detect=1')
And then you have to change rights to /dev/dma_heap to enable video group to use the camera.
I've done it and it works.
Could at least, archlinux arm provide libcamera ? I can understand that the "apps" may be too specific but it would be a great relief to rely on libcamera directly from the repo.