How a Twitter account with a cat avatar took on Beijing
https://edition.cnn.com/2022/12/10/china/china-twitter-teacher-li-profile-intl-hnk/index.html
At a glance, it seems to be safe to tweet from outside Mainland China. But, when the user's relatives are identified by police, it must be a serious case.
So, the best way to tweet under completely safe condition is to rely on old immigrants who no longer have relatives in China.