Currently, all iOS and iPadOS browsers need to use the same engine as Safari.
ANDREW CUNNINGHAM - 2/7/2023
Companies like Google, Mozilla, and Microsoft have versions of their web browsers on Apple's iOS and iPadOS App Stores, but these versions come with a big caveat: The App Store rules require them to use Safari's WebKit rendering engine rather than the engines those browsers use in other operating systems.
But that could be changing. According to The Register, Google and Mozilla have recently been spotted working on versions of Chromium and Firefox that use their normal Blink and Gecko rendering engines, respectively.