I was running 11.2 (20D64) on my 2014 MacBook Pro. I updated to 11.2.1 but the About box still shows 11.2 (20D64) and it now shows no updates available. It does not seem possible to get 11.2.1 on this system now.
Try restarting into Safe Boot, then restart. Open the Software Update panel in System Preferences and press Command and R (make sure to click inside the pane first), which forces a reload of the update pane. This might force through the update.
Question to the forum: shouldn't there be a combo update available for 11.2.1 by now? Or at least a standalone installer like previous macOS updates?