Maybe the reason the update fixed it for OP is that his first launching Xcode after the update wasn't the same method as before, thus clearing this cache. So any update would fix it for me as well, but not because the update contains a fix for this bug, but because the bug is in the post-update first-launch codepath.

I already have Xcode 26.0.1 (17A400) and the problem occurs. For me, it only occurs when I do not open Xcode directly, but I open an xcodeproj or an xcworkspace in Finder or Spotlight. I think when my Xcode has last updated itself, I launched it with this method so it had to perform 2 tasks at launch: download additional components and open the specified project. So I speculate that it has cached an instruction somewhere to open the Downloads window after launching a project and that cache has erroneously persisted. I haven't yet managed to figure out where that cache is.

Here's what helped in my case. What I was trying to do: Insert a file url into NSDocumentController's recent document list programmatically. It was originally opened by NSOpenPanel on an earlier run but then its path was saved to a file for opening later. My application manages the recent list manually based on its own records. What happened: It appeared in the File menu recent list, but Clear Menu remained grayed out. I got the "Insert failed for list identifier com.apple.LSSharedFileList.ApplicationRecentDocuments" error message What caused this: The application was not permitted to access the file that I was trying to insert into the recent list. What fixed the problem: I had to read in the bookmark that I saved on the earlier run, and call startAccessingSecurityScopedResource on it, before inserting it into the recent list. Even after inserting into the list, the app should not call stopAccessingSecurityScopedResource, until the item is removed from the recent list.

Experiencing this in Hungary again, too. As before, not on every machine.