My husband has moderate dementia. After dinner he tends to get irritable, say unkind things, and will confuse what state he is in.

I’m sorry that your husband is experiencing sundowning, I’m sure it’s an incredibly frustrating experience for the both of you.

I’d recommend trying to complete any personal care earlier in the day, limiting any naps/caffeine so he goes to sleep earlier, keeping your home well lit in the evening and keeping a schedule/having activities in the evening.

Please remember to take care of yourself as well. Best of luck and many prayers.

There is no "talking sense" to dementia.
There will be these times.
There are some few things you can try.

I would watch a whole ton of Teepa Snow videos on communication, and participate in some Forums with folks, perhaps even find a support group. This may help in finding/learning little tricks of deflection. You already know the time when trouble is on the horizon. For many it is a sort of "sundowner" thing. So you are ahead of the game.

Try for some activity of diversion, either a great program he loves to watch, a simple game you can play together, a puzzle to put together, anything to deflect from what is becoming a habit in his brain.

Your husband is probably experiencing what is called sundowning, which happens later in the afternoon and early evening. You can Google that term to learn more about it and of course ask his doctor what medications may help with that.
And of course he's getting confused about what state he lives in as his brain is now permanently broken and will only continue to get worse. There may come a time when he confuses you for someone else as well.
I hope that you're educating yourself about the horrible disease of dementia so you're not quite so surprised about the changes that he's going through.
Wishing you the very best as you take this heartbreaking journey with your husband.