Please provide your /etc/pacman.conf (use https://paste.artixlinux.org). Like I said, I tested the plank package from the Arch community repository, and it works with Cinnamon in Artix. Also, if your repositories are ordered correctly (Artix before Arch), it would be helpful if in the same way you provided the file plank.log obtained by using the following commands:
$ pkill plank
$ plank >plank.log 2>&1