Biden was "Sundowning" during the debate.
White House Aides have quietly confirmed Biden is only active as President during the hours of 10am-4pm. If he does anything outside of those hours he seems confused and disoriented like what was seen during the debate. This a common dementia symptom known as "Sundowning".
https://dailycaller.com/2024/06/29/white-house-aides-biden-dementia-symptom-debate/