Second star system
The second star system is the third star system (including Kerbol) in KSP2. Although not announced officially, in the game's code the names Tuun and Qeg were found. It will be added in the Exploration update.
The only information on the second star system is that it will be added to KSP2 right after Deb Deb.
Likely second star system layout
When exiting Kerbol's SOI in KSP2 Early Access 0.01, a phantom Kerbol can be seen in the map view. When zooming into this phantom Kerbol, orbital lines show up which are quite recognizable as the Kerbolar system's planets, however, zooming in further into where Kerbol would be, reveals a second, much smaller, star system. This system contains many more planets/dwarf planets than Kerbol, as at least 9 objects are in this system, with 3 having very inclined and eccentric orbits. This system also appears to relatively be much larger, or spread out.
In one image, a planet is seen. The planet's name is not clear, but the planet seems to be called Axod. It is unknown if this planet is in Debdeb or the unknown star system. Lapat is theorized to be a part of this system because it has multicellular "vegetation" on the surface, which could not have arisen in the very young Deb Deb system. Other potential planets include Puf, Ovin, and the Rask-Rusk binary system.
On February 26, 2023, Two names for two star systems were found in the games code, the Qeg System and the Tuun System, by u/DartFrogYT on Reddit. Nothing is known about these systems other than that they are likely coming in the exploration update or later.