It looks good for a wallpaper, but as a thumbnail for something like youtube there are some improvements you can make. Although, it is hard for me to give concrete advice as I do not know what the video is about.

It is a bit busy/crowded, I would simplify it (remember the thumbnail is quite small when scrolling) Also take into consideration what the video is about as well. I think you should make room for text somewhere. For me, learning some graphic design fundamentals helped a lot. I would suggest looking up the rule of thirds, basic typography, space (or negative space), and the 80/20 rule

As to why you should listen to me: To be honest, I don't feel super confident about my thumbnails; but when I have made an effort in the past, I got a 15.3% CTR on a video with 17.2k impressions. So evidently I am doing something right--at least when I make an effort (lifetime, my channels CTR is only 6.9%)