I don't think the EU DMA changes will require that JIT is supported. Supporting alternative browser engines is something that can be done perfectly without JIT.
Unless I missed something and the DMA requirement is along the lines of "having to allow other browser engines as long as they don't bring their own JITting Javascript engine", no, it literally can't.
And you know, you’re one web search away from finding the page where Apple directly mentions access to a JIT for alternative browsers: https://developer.apple.com/support/alternative-browser-engi...