Biden will be drugged up. The sundowners will make him aggressive and combative. I am thinking that Trump’s plan is to remain calm and professional and let biden be biden.
CNN will edit the hell out of the event to make biden look calm and professional to use in campaign ads.
Trump will have to mention that he is debating the moderators in the debate. He shouldn't answer each question directly from one of the moderators (Jan 6., climate change, "democracy" in USA), instead he should take a page out of Vivek's playbook and talk about how he'll "fix things" like inflation, economy and Russo-Ukrainian War.
That is what he should do. If Trump does want to suggest that Biden's not all there he should do it in a subtle way. For example if Biden says something that made no sense, when it's Trump's turn to speak he should repeat it word for word and say "What the heck did that mean?" and then go on to answer whatever the question is.
But if Biden never presents him with the opportunity it will mean they got the drugs right. In which case don't say anything. He can't force it.