https://www.bleepingcomputer.com/news/microsoft/windows-10-screen-sketch-update-fixes-blurry-screenshots-for-insiders/

A new version of the Screen Sketch app has been released that fixes blurry screenshots and an issue with updating the app from the Microsoft Store. This release brings the Screen Sketch app to version 10.1806.1901.0 and is currently only available to Windows Insiders running a preview build.

Insiders have been reporting to Microsoft that when they use Screen Sketch to take screen shots, the resulting images were coming out blurry. According to Microsoft this new build resolves these issues.