Hello,
1) I passed the issue with the vc-backend-actions-js to our developers.
2) Page score goes down after the import because the page includes a lot of elements, images. Theme and other plugins start to call scripts and styles to show content. If you test empty page, of course, it will give you better results than the page with the content. That’s why you need to optimize images that you plan to use on your page (https://imagecompressor.com/), reduce the number of sliders if you don’t really need them because sliders use a lot of additional scripts as a rule. Don’t add a lot of elements to the page to avoid increasing the DOM structure etc.
3) Could you, please, tell me what errors do you have with the PHP 8? Provide screenshots for better understanding. Or better link to page where you have them. We’ll check them in more detail and fix.
Regards