The virus outbreak brings many risks that are not.

请问这个that are not在这儿是什么使用方法？表示程度的加深吗？

that are not 为定语从句修饰risks。但are后缺少了表语，并且为句号，就说明承前省略了表语形容词。你需要做的就是往回倒着看，找一个系表结构，那个系表结构的表语就是这里省略的表语。

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.

目前你应该了解了 are not后面省略了measuable and quantifiable.

冠状病毒的暴发带了了不少没办法测量和定量的风险。