Steps to take to not escalate. Irritation in an elder who is insisting on something not factual or who wishes to just argue. Father suddenly decides to argue re: bills who he says have come or not, or about meds he's taken or not. Anything can be the topic, but in his confusion, it is difficult to decide how much to engage with him on an unreasonable topic.
https://www.agingcare.com/search.aspx?searchterm=detach+when+parents+get+unreasonable
Develop a bunch of phrases "I'll look into that". "that's interesting, I'll have to think about that". " Can I take care of that a little later, here I'll write it down so I don't forget.".
Pick your battles. Discuss medications with his doctor, does he need to be on as many as he is? Can you keep a chart and have him make a checkmark himself when he takes something? It might be worth a try. But you can also drop it and try 5 minutes later.
I remember once my mom had just been given her pills by an rn who was still seated at her bedside when my mother announced "you know, I have to manage all my pills myself". When I asked what she meant, she pointed to her water pitcher! Didn't know whether to laugh or cry.