The content warning doesn't show up when a tweet that has one is embedded. It's not a perfect implementation at this point. It's a relatively simple process that forces anyone who wants to take a look at your posted media to manually click past a prompt first. The company confirmed on Friday that Twitter users accessing the social media platform on Android, iOS, and the web can now add content warnings to any photos or videos attached to their tweets.
Twitter's 2021 test of user-added content warnings was apparently a success.