When do you start worrying that it's more than brain fog? I am 56 yo and generally my cognitive function is good. But there are times that I just zone out. My daughter was talking to me yesterday and I was hearing words but absolutely had no idea what she was saying. She had to repeat it about 3 times (and it wasn't anything complex). Similarly, I was watching something I'm really interested in on TV and after an advert break, I was still watching but it was just there and I wasn't taking it in. I had to rewind and watch again from the break.
My job requires designing complex scientific research projects and I cope with that fine. Just when I relax I lose the ability to focus.