Ghost in it’s standard configuration is really really fast.
Casper theme is also really good.
Did you do any customization to your theme?
What content are you loading, that could take long to load?
LCP (large contentful paint) considers the rendering time of certain “media” elements like images, graphics, videos and such.
Do you have any files of that sort on your page, that are not compressed and properly sized and therefore account for long loading times?
CLS (cumulative layout shift) refers to layout movements on your page, sometimes due to sudden loading elements. It probably has to do with some content you load on your page, that shifts certain parts of your website.
Casper in it’s standard form has 0 CLS.
Are you caching your static files?
Check that by looking at the response header of a static file (css, img etc.) and look for