How to disable Taskbar Thumbnail preview in Windows 10?

Just after writing this question I found an executable file that seems to tweak thumbnails without installing any program. It can be found here: http://winaero.com/download.php?view.27

Just open it and click Disable thumbnails, then Apply

Done.

You don't need to download a program to do this. You can search for NumThumbnails Registry on the Internet and find several answers, some have a program. But the best just refer you to updating the registry.

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Taskband

Change Taskbar Thumbnail Threshold by setting NumThumbnails to 0.

If you don't have a NumThumbnails DWORD, then you'll need to create one.

Remember - updating the registry can be dangerous if you do not know what you are doing. For complete instructions you can see this page here: Answers.Microsoft - How do I change Taskbar icon preview