What do you mean? This is perfectly modern. Material UI and minimal, outline style icon theme. That's all the rage with web devs nowadays. Amazing.

(Not that there's anything wrong with that in this case, that's the Android style after all. But personally I heavily dislike Material UI.)

I would say that this UI is ugly though. Spacing is all over the place, the icons don't look cohesive at all apart from the colors used (for example, rounded vs sharp corners), the yellowed paper looking background color, overuse of bold/italic/colored text (especially multiple of those at the same time), inconsistent display of the same thing (in one screenshot the mailbox name is displayed as "Gmail", in the other as "[Gmail]"). And so on.

But that doesn't mean it's "outdated", this would have been equally as bad 10 years ago.

(I just have a knee jerk reaction to people saying "outdated UI" because usually it's used as a justification to replacing perfectly well designed UI with a worse version just so that it follows contemporary design trends. Cf the Windows Settings app.)