According to a tweet by user “gus33000”, the company has developed a temporary popup message for when users try to open a Silverlight app on a build that doesn't support it.
In the image, we see a popup message that says “Silverlight apps are no longer supported on this version of Windows.” This doesn't necessarily mean that current Windows Phone devices will lose support for applications such as Slack or WhatsApp.
However, this could mean that when Microsoft is ready to launch its new attempt at Windows phone, Silverlight apps might not get support.
Another key point at Microsoft's alleged new attempt is that it won't launch for existing handsets. According to a report by Windows Central, the company will start afresh with Windows phone with UWP at the center.
— Gustave Monce (@gus33000) June 2, 2017
Microsoft's Universal Windows Platform
Should all that prove to be true, and Microsoft launches a new attempt at Windows phone with the UWP at the center, we expect lots of apps gaining a cross-platform version.
Thanks to the Universal Windows Platform, app developers can launch one application that works with Windows 10 on every device. For example, WhatsApp could create a UWP app that works on all Windows platforms.
In addition, UWP has helped businesses optimize how they operate, with employees working on-the-go using handheld devices and laptops.