Use a vpn with a Eu server. More sites like google will show a cookie popup with the “reject all cookies” option.
Reject all cookies if it exists. Otherwise accept cookies and then click on the :
shield icon > cookies and site data > delete (trash icon)
This is super useful when you want to read an article on some news website and it shows a cookie popup.
Librewolf does that by default, among other things. And as thanksforallthefish mentioned, in settings you can whitelist some pages to prevent cookie deletion, if you want to remain logged in.