In arecent Twitter thread, Twitter Support revealed the social media company’s upcoming changes for DMs.
Unfortunately none of these involves the (very) often-requested Edit button.
According to Twitter, this one is in the process of rolling out on both Android and iOS now.

Message reactions also are getting an update, with a long-press function being added in addition to the double-tap.
This function is currently only rolling out on iOS, with no mention of Android or web browsers.
