There were some KPN users who didn’t receive the update yet. Have you received another security update for Android 11? Then the release of Android 12 is definitely delayed for your provider.
There are ways to force the update, easiest would be to switch SIM cards and trigger it. I wouldn’t recommend that this time, though. At least in Switzerland, there seem to be problems related to emergency calls and that’s likely a feature you don’t want to miss on your phone if you really need it.