Well, I fixed the problem by restoring to iOS 26 from new. I tried from a backup but the problem persisted. when starting new without backup, new Siri now works as intended. Worth it? We’ll see. But it works! (i like a fresh start from time to time anyway)

I've encountered a bug where the "Waitlist Joined" status has disappeared and I'm able to go through the "Try New Siri" process, but the actual Siri app is not installed and it reverts to the old style of Siri before Apple Intelligence. If I open the Siri app by typing "siri://" into Safari, it just says "Siri Update in Progress" with no indication on what that actually means. Ultimately it seems like I'm through the waitlist but haven't actually been given access to the New Siri.

Same here - just made a post with the same issue. Still haven't found a solution.