I wrote a toy text editor for fun a while back. I was aware of the 'rope' and 'gap buffer' data structures, but beyond that I had no knowledge of how "mainstream" text editors are put together. I still don't, really, but I feel that I did get an understanding of many of the core problems.

My editor had a modular architecture flexible enough to implement different input modes, including a mostly-complete subset of Vim bindings, and was fast enough to open and edit files on the order of a few hundred megabytes without perceptible slowdown. I'm sure my implementation would have looked insane to anybody who's worked on a real text editor, but I was fairly proud of it myself.

Anyway, I guess the point is that it was interesting and rewarding to navigate the core challenges myself. I'm not sure I would have gotten as much out of trying to understand how a massive project like vscode is put together, since the actual text editing functionality is (presumably) a comparatively small part of the software as a whole.