As I mentioned in any earlier post, I publish Starfinder third party compatible products, and Starfinder is "science fantasy" with great amounts of magic. The Pact Worlds setting is kind of an impossible system of dozens of planets all inside it's habitable zone, and if measuring distances from worlds to the imagined speeds of Drift drives, I can only guess that Drift is sublight speed, so not FTL. As third party, I cannot use the Pact Worlds (I wouldn't want to anyway), and cannot even use Drift drives with the accepted alternate of the same thing being Hyperspace drives. However, I mention that I lean harder sci-fi, much harder than the default Starfinder setting. Magic is still fully incorporated, but the setting isn't as gonzo. To some degree I grasp the "science" part slightly more.
Last December, I published a 39 page supplement called The Planet Builder. It began with me creating one-shots, and not satisfied with Starfinder's default planet stat block, and wanting something more for my own publications. I was visiting a Discord community called Derwood's Starfinder Combat League, where some of it's members are decent designers. I posed the question, how should I develop a better planet stat block and/or rules to create custom planets. Because that community features starship combat training exercises, someone suggested emulating the starship building rules doing so for planets. And I began development of that in that Discord community, somebody on their boards (Carey Dunn), turns out to be an astrophysicist lab technician suggested because among the factors of world building, is determinig it's moons and their influence on the planets gravity and tides, which habitable zone and where within it exists matters too - why not build rules for custom entire star systems. So I recruited Carey to create the tables for generating scientifically viable star systems. I coupled this with a planet point system allowing you to adjust your table rolls to further customize to your needs, then spending planet points you could purchase Resource Stations (orbiting mine processors, for example) which manifest annual planet points to your pool, as well as other extra-planetary structures (orbiting rings, space stations, weapons platforms, Oniell cylinders, etc.) to grow your system over time.
A major development consideration, is Paizo published a deck of Planets, but under it's default premise you can have worlds that are entirely water, no solid matter at all, and other impossible possibilities. While my rules doesn't preclude such integrations, you'd have to replace a planet or moon created in the tables to accommodate more fanciful results. I designed my Planet Builder rules to be fully compatible with Starfinder, yet as a subsystem only, it's versatile and scientific enough to be useful in any other Sci-Fi game system that lacks rules to generate entire star systems. In a way, it goes against the Starfinder default grain, but I don't care - it's what I needed, so it's what I created. Thus it cannot possibly fit every Starfinder GM's default, it does fit some, and for referees of other game systems than Starfinder, possibly. It was a design choice.