Thumbnail Live Previews in Windows 10 Issue

Hi, have a look at this first: (it shows how they may be disabled- see below)
Change Delay Time to Show Taskbar Thumbnails in Windows 10

noting:

If you use a very long delay time (ex: 10000 milliseconds) it will effectively disable taskbar thumbnail previews.

- so please check the registry key referred to.

What is your Windows build number (as prompted by the forum when you wrote your post, so we don't have to keep asking)?

History: (so often omitted by posters):
- how long ago did this start to happen?
- what change have you made that might have led to this?

Have you tried using a system restore point?

I see, I understood you to be saying it did not show the thumbnail...

but Windows 10 does not display .... the thumbnail

but actually your problem is that did and does show the thumbnail but when you hover over it the maximised window corresponding to that in the thumbnail isn't shown?

Or do you mean the maximised window is shown, but you would additionally like not to have to click on the thumbnail?

If this has only just started to happen, you could try using a system restore point, but perhaps you are unsure as to when it started.

Please have a look at this and check your registry keys and values:
Change Taskbar Thumbnail Live Preview Hover Delay Time in Windows 10

noting

If you set a high delay time (ex: 1000000 milliseconds), it will effectively disable taskbar thumbnail live previews without having to turn off Peek at desktop.

Use the System Restore point.