I’m not worried about the nothingness after I die. I’m anxious about the impending loss of enjoying my wine.
Have you ever been to a party and it started winding down and people left and you wanted them to stay and the fun to continue? That’s the anxiety.
What I believe is, you probably won't actually ever have to stop drinking wine. From your perspective, I'm not sure it's meaningful to say you'll ever stop existing, because you can't experience it. You'll (probably) just stop existing for me, and I for you.
It's fair to be sad about it just like I'm sad that the elves left Middle Earth at the end of the Third Age. But neither my own death nor the leaving of the elves is something I can ever actually live through - they're both just stories to me.
It's unpleasant, and it's difficult to imagine, that doesn't mean you should be anxious about your own death.
Again... from your subjective experience, I'm not sure it's even meaningful to say that you will die. You will only ever experience being alive.
You can't even be sure that the universe will continue after your death, either. Does it seem most likely that it will? In some models of the universe, it's actually infinitely more likely that it won't, because it all exists inside your (Boltzmann) brain.
Like what is the specific thing that causes anxiety? That's still not clear to me. Not-knowing, yeah, that can cause anxiety. And it can be soothed by changing your perspective, taking delight in the mysteries of existence. We all have a visceral anxiety about death which our bodies evolved to have, because it's quite useful for a living thing to want to stay alive. But that's not based in reason, and we can use reason to alleviate our anxiety.