The whole pumping his face full of botox, bronzing his skin and putting fillers around his eyes is a terrible idea. His facial muscles are so sedated that his facial expressions genuinely look dead. They need to stop trying to pretend he isn't old and making him "look vibrant".
That isn't how negotiations at that level work. Most of the details are sorted out long before two world leaders meet face to face. When they do finally meet, translators who are involved are expert negotiators and diplomats, who have gone through weeks of preparation with the president and the state department.
Every call has 3-5 experts sitting in, with their staff, some are in the room with the president.
The biggest hurdle for success in negotiations with foreign leaders is the president's ability to pick the best qualified advisors, know what can and can not be done, understand the reports his staff presents and understand the underlying politics. A president that approaches negotiations like "one on one" business negotiations will fail, break the law or make huge diplomatic blunders (for example quid pro quo) - see Trump's presidency.
Biden's age and verbal slip ups are of no consequence to his ability to be president in those situations. His "strength" in negotiations come from the power of the country, his choice of cabinet staff, and his understanding of political manoeuvrability, not his personality. That is why Biden managed to unite NATO, prevent a huge escalation in the middle east, de-escalate Taiwan, increase support for Ukraine globally, coordinate a global effort against COVID and ensure huge foreign investment in US tech.
There isn't a person alive more qualified for the job than Joe Biden, the big question is whether or not he is a good enough candidate to get reelected.