My Samsung s20 Ultra 5g, is still running on android 10. And last security update was September 2020. I've been in touch with Samsung who have told me to factory reset and clear cache. And still shows I have the latest software?
What is your device's CSC? You can find this by going to settings>about phone>software information, it will be listed under service provider software version. It will be a three letter code, mine is BTU which is the factory unlocked CSC code for the UK.