Checking for Updates stuck on iMac - not showing latest Update available / Im on macOS 10.15 still

Hi all,

Im currently on macOS 10.15 and im not able to update my iMac to the latest one (not sure what it is) - im checking for updates and know it needs updating but nothing is showing up even after 30-40mins.

I have enough storage and Internet connection is fine too.

Any advice will help! :)