https://www.vice.com/en_us/article/bvneym/elon-musk-reading-twitter-dms-direct-messages

With the acquisition of Twitter by Elon Musk, a billionaire with a well-trodden track record of going on vindictive triads against his critics despite his declared adoration of “free speech,” some people have raised concerns about the privacy of Twitter’s direct messages once again.

Twitter’s direct messages are not end-to-end encrypted, unlike messages from more security focused services such as Signal. With end-to-end encryption, the service provider is unable to read the content of messages because they are encrypted on a user’s device and not by the site’s server itself. Sites like Twitter, at least theoretically, which don’t have such robust encryption run the risk of someone inside the company being able to access those messages, depending on the specifics of how that company has set up their systems, at least.