Step #1 is to read the stickies at the top of this sub-forum. In particular, read
https://www.mobileread.com/forums/sho...d.php?t=118605
Your source PDF contains nothing other than images. Each 2-page spread is a single image. There are no "conversion settings" that could possilby yield any better conversion of the existing PDF other than, perhaps, enlarge the images to better fit the screen. You will still have 2 pages per image.
It's possilble to open individual PDF pages (a 2-page spread) in some image editors (e.g. Photoshop) and split them into single pages and save a JPEGs. If saved and named correctly they can then be imported into calibre as a set and converted to an ebook format (e.g. ePub, Mobi, ...). If the JPEGs are sized well and contrast adjusted in the image editor the results should be better than you're getting now.