robots sitemap many languages, to see if no content shifts black is hard to read design in black and white, to not be bothered with colors. yslow try to print the page use real data https://designschool.canva.com/blog/design-rules/ does it have vector graphics?
do you have “share” part do you have a visit counter? do you have analytics? do you have blocking JS/CSS/ is your website compressed
It’s important to test your website on mobile, since soon there’ll be no desktop computers, since new users with tablets and smartphones don’t want to bother with laptops.
If it’s ugly, nothing will help.
Use Google WebPageTest and Pagespeed to test your website.