Review all languages for missing translations (buttons etc)
Check mobile icons (favicons / apple-touch-icons) are added
Review images for final edits / positioning on all devices
Review need for mobile specific images
Check 404 page
Check all navigations are logical (semantically and structurally) in both large and small screens
Test forms: make sure the right email recipient(s), integrations are working, thank you messages are human.
Confirm social share images are in place. Test with Facebook debugger (+ LinkedIn Post Inspector)