How to improve thumbnail quality?
The aspect ratio of a thumbnail has to be square.
The model in the thumbnail must not be cropped around the edges and should fit completely into the thumbnail.
If possible, leave some space around the edges. By professional photographers this space is called “air”, since it allows your model to breathe. When you have air, the model won’t look as if it is stuffed into a box.
Plain color background usually works best.
You are welcome to use the BlenderKit internal thumbnail generator.
There are some examples of great thumbnails below.
Thanks and enjoy your fresh thumbnails!