What aspects of your product must be flawless before its release?

I guess the product's essential features and functionality must work without severe faults or bugs

First of all, these are UX and UI.

Make sure the product is compatible with a range of platforms and browsers.

Include mechanisms for users to report problems or offer feedback.

Content, design, and functionality.

Absolutely nothing :)

Basic functionalities and the UI

Stability, new products are usually more buggy, so I think it's very important to keep it stable so that you can get valid information from your seed users

The key feature of your product.