Snip and Sketch disabling over GPO
Solution 1:
You can use AppLocker and Packaged apps and packaged app installer rules. Typically, you can create a rule to allow every signed appx, and add an exception for this app.
Solution 2:
I am not sure what the end goal of disabling snip and sketch would be, people can still just hit print screen and paste into MSPaint, or take pictures of the screen with their phones. As a security concern it seems a little... fuzzy.
You could however just remove it from peoples computers -
Get-AppxPackage PackageFullName | Remove-AppxPackage