No Software update found in app store?

Hello, I'm running iMac 27" Late 2013 Sierra 10.12.6

I clicked on software update tab(in the "about this mac") and it takes me to the app store, but there is no updates for software. What am i missing here? I know I cant go higher than catalina 10.15 but do i have to type in catalina in the app store? i assumed it would automatically be seen in the updates area.

Thanks