Quick answer: On Nov 3 the Steam Deck's Steam store page redirected to the Steam homepage while Valve's other hardware stayed listed, and Valve hasn't explained it or announced a discontinuation. By 5:35 PM ET the page was loading again from a US connection.
For part of Nov 3, trying to open the Steam Deck's page on the Steam store just dumped people on the Steam homepage. PC Guide said the page was missing at least in the United States, the United Kingdom and Europe, while the Steam Controller, Steam Machine and Steam Frame stayed available.
MIXED saw the same thing. The Steam Deck still showed up on Valve's hardware page and in Steam's hardware search, but both the buy link and the search result sent them back to the homepage. Valve hasn't explained the redirect, and it hasn't announced that the Steam Deck is discontinued. MIXED points out that the redirect alone doesn't show that, and that it could be a store problem, an inventory change or something else.
Valve's Asia partner Komodo Station, which covers Hong Kong, South Korea, Japan and Taiwan, still had listings up according to PC Guide. In Japan it shows the 512GB Steam Deck OLED at ¥137,980 and the 1TB model at ¥167,980. Valve already stopped selling the LCD Steam Deck, so the OLED is the only model left. The Steam Deck 2 hasn't been announced, though a possible chip leaked in October.
When we checked at 5:35 PM ET on Nov 3 from a US connection, store.steampowered.com/steamdeck loaded normally again. It listed the 512GB OLED at $789 and the 1TB OLED at $949, both with a Buy Now button and an estimated delivery of 6 to 10 business days. Those match the prices Valve set when the OLED came back in stock in May, citing higher memory and storage costs. Valve still hadn't said anything about why the page went missing.