I think the ideal limit as far as complexity with no manual coding would be something like this new marketing site for my game (warning: 100mb of video on Chrome): https://redo--fallofanempire.netlify.app/

Cursor with Gemini 3. I didn't manually write a single line for it (except for the actual wording). Gemini did the React stuff, styling, writing ffmpeg commands for re-encoding the videos to work better with scroll-based scrubbing, splitting them out into AVIF image sequences for mobile, etc. I use Cursor + Codex for the actual game as well but it involves a lot of manual work - even with a really modular system like Unreal it gets convoluted.

I tried doing a spreadsheet application heavily using Sonnet 4 (https://app.embedsheet.ai/) and found it would make a ton of mistakes and massive files that it would then be unable to reason with, I think if I did it again I'd do all the core stuff by hand.