Welcome! Stuff like this usual goes in the How Do I section, but this is fine.
It's a little more advanced, but you would take a Snapshot (system action in events) then apply something like a WebGL shader to it and change the parameters over time. So it would get more swirly or whatever until you fade it out with changing opacity over time. Then destroy the screenshot sprite you just made and you're done.
Here is the manual entry for taking a snapshot:
Take a screenshot of the current display. This triggers On canvas snapshot when the snapshot is ready, and the resulting image can be accessed with the CanvasSnapshot system expression. This can then be loaded in to a sprite or tiled background, sent to a server, or opened with the Browser object in a new tab.
So just apply it to a sprite, place the sprite over top of everything, change an effect parameter over time.