The alien observatory door in Subnautica 2 is fairly close to the Alien Ruins biome/marker, which is a key objective once you’re done with the Tadpole Pens. If you’re just free-roaming, then the ...
A series of Blackbox Signals scattered about the world in Subnautica 2 act as a questing throughline of sorts.
Here's how to fix the Translation Failed notice when you hover over the alien symbols in Subnautica 2.