[2022] Surviving Mars - Project Laika content not appearing

New content will not be available in existing games. Did you start a new colony since installing this DLC?  

According to the wiki

Project Laika - Surviving Mars Wiki

survivingmars.paradoxwikis.com

Once you terraform the planet enough, pets will go outside to explore nearby bushes and trees.

I don't know the threshold for them to appear, but I guess you haven't reached it yet.