The Bioscanner is a very important late-game upgrade to your trusty Scanner in Subnautica 2, since it lets you scan marine life to unlock additional Biomods. I recommend you grab it as soon as you can, as unfortunately the scans aren't retroactive. You'll have to find and scan any creatures you might have already catalogued.
You'll need to have reached the Alien Ruins area, which comes after completing the task at the Tadpole Pens and crossing the large, open stretch of ocean. After that, I recommend you grab the Depth Module for the Tadpole so you can explore this area without getting crushed by the pressure of the deep sea.
