If he starts the conversations he seems fine,he can answer questions, discuss back and forth, listen and respond, but I have noticed the word thing being used a fair amount when he's forgotten what something is called but he does it very smoothly,if you're not watching for it you wouldn't notice/ think anything of it.
If you start the conversation even if the same as he started,he struggles to respond,get involved.
It isn't consistent either, he can go a week seemingly perfectly fine,then you get days where he doesn't seem able to follow anything, just blank face most of the time.
I think the latest streak has been because we had to isolate (had a covid case in house) and it threw his routine, we have a dog who he is OCD about, he has to walk her,no one else does it correctly, he wakes even a little during the night he is up and taking her, even if 3am,he can't roll over and go back to sleep because he's just got to take her, she's waiting for him to take her for her walk. Anyway he couldn't take her due to having to isolate ( but I did catch him coming back after walking her at 5am on day 2 of isolation,but that's another story) and he couldn't settle as he felt constantly like he should be doing something and it just spiraled from there