I dont think there are any biologicals to scan in the starter system, although I could be wrong. There's no way that the single starter system out of all the billions of systems will have too much variety in it, I think you will need to venture out.
And do exobiology things to scan show up as a marker like any other feature after using DSS? I haven't found anything.
If other features are showing up, I'm guessing you're not using the DSS, just seeing points of interest and ground sites in your left panel? The Detailed Surface Scanner is for firing probes at a planet which returns the blue 'heat' map that shows where biologicals are and what they are.
But in the bubble you don't need to DSS the planets, as it's all been discovered, unlike outside the bubble. If you go to the system map and look at the planet information for every planet it will tell you how many biologicals there are, they are already known in already discovered systems. You can still scan them and get cash, and go through the gameplay loop of locating and scanning 3 samples etc, but you wont need to DSS the planet to know they are there.
If you were to go back to Horizons you miss out on landing on atmospheric planets and just more interesting places to land. (shamelessly stealing from
Alec's thread)