The virus outbreak brings many risks that are not.

請問這個that are not在這兒是什么使用方法？表示程度的加深嗎？

that are not 為定語從句修飾risks。但are后缺少了表語，并且為句號，就說明承前省略了表語形容詞。你需要做的就是往回倒著看，找一個系表結構，那個系表結構的表語就是這里省略的表語。

原文如下：

t is also possible that the virus spreads rapidly outside China. Infections in developing countries may be going undetected. Vietnam has quarantined 10，000 people， but most governments could not enact the measures that China is using to slow the disease， so covid-19 could yet become a pandemic. Wall Streets optimism， in other words， is premature. If economists have a bias， it is to focus on things that are measurable and quantifiable. Alas， the covid-19 outbreak brings many risks that are not.

目前你應該了解了 are not后面省略了measuable and quantifiable.

冠狀病毒的暴發帶了了不少沒辦法測量和定量的風險。