So many videos have amazing thumbnails. One way to learn how to copy this style is to download the picture for yourself and practice.
So here it is. The most simple easy to use Youtube Thumbnail Downloader!
Go to this website https://ytthumbnailgrabber.com/
Copy the Youtube Video URL that you wish grab the thumbnail from and paste it into the search bar on the website.
You will now have 3 options to choose from ranging from SD to HD!
I hope this helps you out guys.