Restore "tooltip" full window title instead of preview.
What annoys me most about the previews (aside from the pointless resource waste and "noise") is that hovering active buttons used to usefully tell me what the full window title is. It rarely fits in a button even when the text is shown. Now Microsoft have made no text default and full text impossible.
"The Microsoft giveth, and he taketh away." :(
Maciej Katafiasz commented
Hovering over a thumbnail for a moment will show you the full title. Is this not what you want?