Check if the website is mobile friendly. We need to check the website with different mobile phones with different screen resolution, Android and IOS etc.

Website should be accessible with only one version - www/non-www/http/https. Use redirect checker tool like https://www.redirect-checker.org/ and check each version at a time and check if that is redirected to the right version or not.

Redirects: Check if 301 or 302 urls are there in the website. Also check redirect chain. Use screaming frog - https://www.screamingfrog.co.uk/redirect-checker/ or https://httpstatus.io/

Check the indexed pages. Type site:yourdomain.com on google