Apple could be working on an iPhone prototype running a full-fledged macOS, according to insider information cited by Mauri QHD. While there is no way to confirm this, such a possibility is not a distant dream given that Apple has begun transitioning its entire lineup to ARM. If this news is indeed true, it remains to be seen how effective would be its implementation considering that previous such attempts by competitors haven't been too successful.
https://www.notebookcheck.net/Apple-rumored-to-be-working-on-an-iPhone-running-macOS-and-is-apparently-very-excited.477590.0.html