Heh, many years ago I actually started writing a dedicated diff viewer app for Android [0] that specifically had synchronized horizontal scrolling between the two sides, and I remember finding it relatively usable in landscape, and I’m sure modern phones with larger and higher density screens would be even better.

But yeah, you definitely need a native experience to make side by side diffs viable on mobile.

[0] https://github.com/scottbez1/superdiff — I wish I had recorded some videos of the app back then. My code review workflow back then eventually stopped including diff attachments on code review emails, so I abandoned development on it.