Samsung discontinues its mirroring app for smartphones2
Ironically, Samsung added support for Android 9.0 Pie early this year, which suggests that the decision to discontinue SideSync was probably taken more recently. For those unaware, the SideSync app lets users share their smartphone's screen and data with a tablet or PC.
As TizenHelp points out, instead of SideSync, Samsung now recommends Galaxy smartphone users to download Samsung Flow, an app that does exactly what the soon to be discontinued SideSync app does.
Effective October 15, Samsung SideSync will no longer work, so if you want to be able to share your smartphone's screen with your PC or tablet, you'll have to switch to Samsung Flow.