When it comes to testing pages using Lighthouse, WebPageTest or other similar tools, cookie and similar consent banners are a pain!
They can cause layout shifts, on mobile the banner is sometimes the element for Largest Contentful Paint (LCP), they visually obscure other parts of the page, and if implemented correctly only some of the page's resources will be fetched.
When analysing sites one of my first steps is to work out how to bypass any consent banners so I can get a more complete view of page performance.
This post covers some of the performance issues related to consent banners, how I bypass the banners, and my approach to working out which cookies or localStorage items I need to set to bypass them.