Yes, technically speaking, there are a few ways to download a 4K thumbnail from YouTube by improving image quality and ultimately convert an image to 4K resolution. Learn how to enhance your YouTube thumbnail to 4K resolution with this step-by-step guide:
Use above tool to save the YouTube thumbnail in HD resolution.
Visit a 4k Image Converter website.
Utilize the "Enhance Image" button to upload the previously saved image.
Apply the AI Upscale 4X option on the uploaded image.
For optimal compression, select the PNG image format (other options such as JPG, BMP, and WEBP are also available).
Convert and save the image to your device.
The final result will be an enhanced 4K image with a resolution of 5120 X 2880 pixels, while the compression will lead to a large image size.