Why often there is no screenshot for purely visual things?
There's one screenshot in their blog [1]. Unfortunately, it's not clear from the announcement just how flexible this is. It would be fun if it's capable of effects like cool-retro-term[2].
(EDIT: There was a "retro terminal effect" released a year ago, and the announcement for that version [3] shows it affecting the whole window. A quick search through the Microsoft Terminal source suggests this new feature is an extended version.)
[1]: https://devblogs.microsoft.com/commandline/windows-terminal-...
[2]: https://github.com/Swordfish90/cool-retro-term
[3]: https://devblogs.microsoft.com/commandline/windows-terminal-...