the Website Grader is great but unfortunately doesn't provide you more informations.
Once you check the page with google page speed/lighthouse (Website Grader uses it) you'll see a lot more infos about possible issues.
In your case you've passed the web vitals on mobile but it also tells you that most issues are because of (image) loading issues and JavaScripts(as almost on every page 😀)
I'd recommend to check for loading settings like are the JS getting loaded asynchronosly or defered, if you're using custom modules with images - do you use lazy loading and optimized size settings within the code, are the images uploaded web-optimized (in terms of file size)
Website not responsive according to WebSite Grader
Thank you Anton,
I know this tool but I was courius about this issue with responsive because it's the first time I see a website that doesn't pass it.
About reducing javascript, I already ask to the community about some tool to help to edit it but I understood there is nothing, and editing it by hand can cause the break of some feature. Lighthouse is useful but it focus on the single page, so it's very usual that some code highlighted like not used in reality is very important in another page of for another device.
Can you give me some suggestion to deal with it without broking the website?
For the image, the first one is set "eager". Is there something more I could set?