A testament to the Deck's optimization or Starfield's? Either way, I've definitely experienced supposedly "verified" games on Deck that are middling performers at best. Hopefully this one means 40+ fps on medium settings minimum.
Hard to say given the minimum requirements for the game are much higher than the steam deck (the RX 5700 is a desktop 36 CU RDNA1 gpu, the steamdeck uses an 8 CU RDNA2 igpu). The thing is, theres no standardization of what minimum requirement means, settings, frametarget and resolution wise, hence why minimum requirements are usually not that helpful.