Twitter executives opted to allow Twitter to become more dependent upon revenue coming from Chinese entities even though the Twitter service is blocked in China. After Chinese entities paid money to Twitter, there were concerns within Twitter that the information the Chinese entities could receive would allow them to identify and learn sensitive information about Chinese users who successfully circumvented the block, and other users around the world. Twitter executives knew that accepting Chinese money risked endangering users in China (where employing VPNs or other circumvention technologies to access the platform is prohibited) and elsewhere.
Zach Edwards suggests in a Twitter thread how that may be possible. Long story short: custom audiences for Twitter advertising can be built using email addresses and mobile IDs, which—through some clever tricks of how ad campaigns are set up—would allow to relate those details (which Chinese entities might already have) to sensitive information, like location (which they might seek). At least, that’s how I understood it, you should check out that thread.