Preface: iPhone XS is powered by the A12 Bionic processor. iPhone 13 and iPhone 13 Mini use the Apple-designed A15 Bionic chip system. Additionally, the iPhone 15 is powered by a six-core Apple A16 Bionic processor. All above Bionic processors have common point. They are 64-bit ARM-based system on a chip (SoC) designed by Apple Inc.
Speculation: If you remember, a vulnerability related to AMD on 15th Mar, 2024.(CVE-2024-21930) Specter v1 variant inheriting the Specter v1 vulnerability. So called GhostRace. But this design weakness not only to AMD. For example, ARM Limited do not announce they do not impact with this vulnerability. So, do you think, Apple Inc. might worries about this vulnerability thus in priority to update Firmware and Linux base OS to mitigate this risk?
Official announcement: Please refer to the link for details – https://support.apple.com/en-us/HT201222
CPU hardware utilizing speculative execution may be vulnerable to speculative race conditions – https://www.kb.cert.org/vuls/id/488902