I can not get the Quake II RTX demo to work

[-$ilver-]

I can not get the demo to work. It asks for Administrator permission and I gave it and it asks to download either the demo or the main game. The main game is 0 MB as I did not purchase it. Plus it asks to download manually where you want it to go. The demo just downloads to a Steam folder on it's own. However pressing Play looks like it tries to start, but then does nothing.

I have verified the game and it says it is good, but when trying to play it makes me give permission again and also have me redownload the demo, but the same outcome occurs. I have even restarted Steam, but still does not matter. I have completely uninstalled and redownload the demo again, but it still does not make it work. Any idea of the issue? Thank you.

Edit:
[(Original post asking about the demo)
I could of sworn tonight I had downloaded the Quake 2 demo. The page had even said the first three levels or episodes of the original shareware version or something like that. I believe it was under the free games section or maybe a mod for Half Life (not sure how that was filtered in there, I guess "mod"). But when I checked my library I could not find it. So I searched for it and I found the demo on the Steam store, but when I click on the thumbnail, it takes me to the store page for the full game of Quake 2 and there is no demo that I can see. What happened to it? Thank you.]

[Kaiser Ducky]

On the Quake 2 store page, look at the right hand side. Under the part that says "Is this game relevant to you?" Just underneath that section, you should see a little box that says "Download demo."

Steam Store pages are a bit cluttery. It's super easy to miss if you're not sure where to look. Hope this helps!

[-$ilver-]

Thank you. Apparently I had already downloaded it, but I had also downloaded Half Quake. The demo is marked as Quake II RTX, so I had assumed it was the other game. I also thought the clickable demo link was a larger box, but you are absolutely correct. Thank you again.