@domubpkm I am sorry, I forgot to reply. Sadly so far I haven't found a working solution.
When setting the TextArea to read-only, we can't navigate in it. So no option. I didn't found time yet to see if some manually added controls allow moving the text in read-only mode.
I also tried (after your question, could you please open an issue/feature request so I don't forget about that?) to display the file in a webview. I used that successfully when testing something for weather app and webviews allow pinching and dragging and that.
But for some reason simply instantiating a webview component in the code, not even displaying a file, always crashes tedit (of course no error message that might give a direction where to look at). I am totally lost here why that happens. Many apps use webviews for various purposes.