We're constantly working on improving Universe Sandbox in many ways, including improving its performance.

We're actively working on a major graphics overhaul that uses an entirely new graphics rendering system. While we're still actively working on this, our initial testing has shown a general improvement in performance overall in this new system in most scenarios.

We're also working on major overhaul of our physics simulation engine that we hope will also improve performance in the future. You can read more about what we've been working on and plan to work on this year in our 2024 Roadmap post
https://store.steampowered.com/news/app/230290/view/6501581293008131627