The X300 Ultra will be compatible with the vivo ZEISS Telephoto Extender Gen 2 Ultra and vivo Imaging Grip Kit. The X300 FE will be compatible with the vivo ZEISS Telephoto Extender Gen 2 and vivo ZEISS Telephoto Extender Accessories Set.
Platform lock-in is a thing, and Apple has it better than most. Apple provides an entire ecosystem of devices and cross-device functionality that most other OEMs can't match. It's not that Samsung doesn't have an ecosystem of its own, but Apple's devices are designed from the ground up to work together. They're on a level of detail that other ecosystems -- including Samsung's -- can't really compete with.