Pixel 6a used to show a September patch as the latest, but tapping "check for updates" found a new one. As mentioned in other comments here, apparently tapping those buttons twice may help.

I was clicking "Check for Updates" every few hours. Finally started working a bit ago.

Fun fact: Pixel 7 and Pixel 7 Pro didn't get a November update

Can confirm on a Pixel 6a.

Says September is the latest system update. Click check updates, says it's up to date, click check updates again, says it's preparing system update and hangs out for a while - then says it's downloading and installing a 781M update.

WTF?

Update: OK finally the update completes an hour later, even the reboot took longer than usual - says it's "updated to December 5, 2025"

This phone running Android 16 for a bit over a month now.