Recent Folder Disappeared Suddenly

I believe I've found an answer. In response to a different issue a user suggested deleting dock preferences (com.apple.dock.plist in ~/Preferences). I found I had 4 preference files named com.apple.dock.plist.xxyy. I deleted all, restarted my computer, added Recents from my sidebar to my Dock, and it's sticking. It's been several hours, and Recents is still in Stack mode, still active.

Is spotlight still indexing? Recent is a smart folder, so Spotlight would’ve need to have finished indexing to show anything.

UPDATE: After deleting the Dock preference files the Recents icon in the Dock will remain active and populated for the current session but, at least on my iMac, won't survive a restart.

I believe this must be a bug in the MacOS, at least in Big Sur. I've added a Recents folder into my Dock numerous times. It starts as a Stack, then on its own changes to a folder/drawer. And at some point in time it empties, and I remove it from my Dock. However, the Recents in my side bar still contains all the entries seemingly forever.

If anyone has an answer to this I'd sure appreciate it.