Arnold Render 4.4.0 is compatible with a range of Cinema 4D versions, including R21, R22, R23, and others.
Here is a more formal and tech-detailed article Arnold Render 4.4.0 for Cinema 4D R21 R22 R23 R...
As with any software update, there may be known issues and limitations. Please refer to the official documentation and release notes for more information. Arnold Render 4