Games like X Rebirth
Games like X Rebirth include X4: Foundations, Elite Dangerous, No Man's Sky, Kerbal Space Program, and Stellaris. We matched them by the tags players give X Rebirth on Steam (Simulation, Space, Sci-fi, Action, and Space Sim): closest matches first, and among equally close ones the better-known games.

X4: Foundations
Shared: Simulation · Space · Space Sim

Elite Dangerous
Shared: Space · Space Sim · Simulation

No Man's Sky
Shared: Space · Sci-fi · Open World

Kerbal Space Program
Shared: Simulation · Space · Sandbox

Stellaris
Shared: Space · Sci-fi · Simulation

EVE Online
Shared: Space Sim · Space · Simulation

X3: Terran Conflict
Shared: Simulation · Space · Sci-fi

SPORE™ Galactic Adventures
Shared: Simulation · Space · Action

Rebel Galaxy
Shared: Space · Sci-fi · Open World

Endless Sky
Shared: Space · Sci-fi · Simulation

Starfield
Shared: Space · Sci-fi · Singleplayer

Space Engineers
Shared: Space · Simulation · Sandbox

Hardspace: Shipbreaker
Shared: Space · Simulation · Sci-fi

Dyson Sphere Program
Shared: Space · Simulation · Sci-fi

SPORE™
Shared: Simulation · Sandbox · Space

Jurassic World Evolution
Shared: Simulation · Sandbox · Sci-fi

Avorion
Shared: Space · Sandbox · Space Sim

Kerbal Space Program 2
Shared: Space · Sandbox · Simulation

Starpoint Gemini Warlords
Shared: Space · Simulation · Sci-fi

Empyrion - Galactic Survival
Shared: Simulation · Space · Space Sim

Starpoint Gemini 2
Shared: Simulation · Space · Sci-fi

STAR WARS Jedi: Survivor™
Shared: Action · Singleplayer · Sci-fi

Starminer
Shared: Space · Space Sim · Sandbox

Fallout 4
Shared: Open World · Singleplayer · Action