Backdrop filetype

[prochri]

First up, thanks for the great work!

I currently have a keybinding, which closes all floating windows except for the focused one and some exceptions I can set.
With a very recent update, the Lazy window now has a backdrop floating window with no filetype set.

Is there another way to detect this floating window (which looks very cool btw) or could you set the filetype for this? I could probably also come up with a PR if wanted.