I am afraid that if the image source is a bad quality image, there are not much you can do!
I think this image is by default a 300x168 image so bumping it up to 800px will certainly make it only worse!
I would recommend searching for a better quality image, maybe on sites like pixabay.com that they are free to use.
I’ve edited your post for readability. When you enter a code block into the forum, remember to precede it with a line of three backticks and follow it with a line of three backticks to make easier to read. See this post to find the backtick on your keyboard. The “preformatted text” tool in the editor (</>) will also add backticks around text.