This, as I've explained several times.

On the face of it, there is nothing wrong with Ian Coleman's site. It is a useful tool, and one I use myself for exploring seed phrases and derivation paths. But javascript entropy generators are not secure. Although the site produces 128-256 bits of entropy (depending on how many words you select), I am not convinced this entropy is securely generated, and so provides less than 128-256 bits of security.