When discussing elections, "certified" without qualifications (or, equivalently, "legally certified" or "officially certified") conventionally refers to formal action by the government entity overseeing the election results declaring them legally final (potentially, pending certain appeals), whereas "independently certified" refers to a less formal declaration of the results by a third party other than the candidates and their proxies or government administrators such as election observers or independent media outlets.

Waiting for the election to be "independently certified", which is what Biden was asked about, is a very different thing than waiting for it to be "certified" without qualification.