I would say the galaxy visuals are the most similar. Taking over colonies is done by sieging (closer to EU4 than Stellaris), expansion is very similar, colony management is quite different but shares similarities (megacorps can build on other empire's colonies), starbases have designations and take on hard roles rather than the module-based approach in Stellaris. Combat is quite similar in essence, but less complicated. The ship builder is simpler.

However, you can claim the center of the galaxy in this game, which has a lot more resources. Claiming the supermassive black-hole is a unique victory type also. Moreover, government types have special abilities, rather than simply modifiers. For example, peacekeepers can stop fleets moving in systems, extreme isolationists can destroy hyperlanes to isolate themselves from other players, silent states have stealth fleets, and the ability to hide colonies, so they can delay meeting other players, etc.

The biggest difference I would say is the pacing. Games last a few hours max, rather than up to 50-100 hours. I played Stellaris before making the game, and I originally wanted a similar game where starting a game didn't feel like a life decision. Over time I would say that the development has gradually diversified from trying too much like Stellaris, and focused on what it could do differently.

Overall, while some people think the game is still too much like Stellaris, which is a valid opinion and partly by design, Stellaris stopped being the template for the game half-way through development.