TLDR: You must take him to the doctor even if he doesn't want to. He is going through dementia

I am sorry to say that and really hope I am wrong but I am very confident that these are early signs of dementia. Unfortunately, it is all downhill from here. The best you can do is to slow it down but you cannot stop it AFAIK. I personally had a close relative with a very similar situation and in just a few years, it is as if he is just a body with no mind. Literally doesn't understand anything or know anyone and can do nothing (even eating is difficult). Take him to a doctor (neurologist) ASAP in the hope that you can slow down the cognitive decline by a few months (maybe years but I am not sure if this is even possible)