Back in March 2017, YouTube announced that it would be removing annotations, the pop-up boxes that appear during a video with links and additional information. Two months later it discontinued the annotations editor and said soon all existing annotations will go
YouTube recently added an update to the help page announcing the end of its annotations editor, saying, "We will stop showing existing annotations to viewers starting January 15, 2019. All existing annotations will be removed," reports engadget.
Annotations didn't work with mobile and in response to video creators' call for annotations, YouTube created Cards instead. It also introduced End Screens in 2016, and as those two features became more popular, YouTube said annotation use decreased by more than 70 percent. The company says that compared to annotations, Cards and End Screens are more engaging and easier to create, along with being functional on mobile.