I believe I also saw that they were using glass graded for 1300m max for the viewport.
...for a 4000m dive.
Even if the oxygen supply wasn't an issue, I can't imagine that the thing hasn't shattered by now.
I swear, this was all an elaborate ploy to get rid of rich people, because nobody would actually put together a vessel so unsuited for the task.
I would barely trust true to form meticulously engineered and tested military SSBN submarines like the Ohio Class or Delphin Class to take me several thousand feet underwater. Forget a literal welded tin can with a PS2 controller.