Personally I'm not a fan of it because there's a lot of contrasting colours making the overall design quite busy. BUT considering the world isolation right now, I understand we can't all be making brilliant thumbnails right away.
I can't understand the language, so based on the fabric in the background, I'm going to assume this video is about sewing of some kind? Also, the person to the right is hidden in shadow, this can be fixed if you rotate both you around to face what seems to be window lighting.
I'd get in closer together and zoom right in on your faces and the fabrice. I also think there's too many colours in the text, and the text boxes aren't aligned.
If you did all the text with the black and yellow only, or the green and red only you'd have more consistency and it wouldn't look too scattered.
Also, you don't have to rely on a screen capture for the thumbnail. You can actually take a seperate photo specifically for the thumbnail.
But at the basic level, I'd zoom in more on your faces and a bit of the fabric.
Over time the thumbnail is growing on me, but on first impression it needs a bit of work.
Hopefully I've given you something you can use to improve it