None of the Chinese fonts included in Discourse’s built-in font settings are pleasing to the eye, but fortunately you can easily override the default font settings via the custom CSS feature.
:root {
--heading-font-family: inherit!important;
--font-family: inherit!important;
}
The inherit setting here means using the font from the parent element (i.e., the browser’s default font), and you can also modify it to any other desired font, which will take effect after saving.