how do I update my MAC when it says no update, but hasn't been updated since 11/19

If you are running 10.13.6, then there are no more updates. You can only upgrade from High Sierra to Catalina if your model is supported. See How to upgrade to macOS Catalina.

Hi, welcome to the Apple Users Community.

You are running El Capitan, yes? Which is not supported any longer, there will be no more updates to this OS but you have the option of updating to:

High Sierra which will be phased out of support when Big Sur launches soon.

Mojave

and be very careful that your MacBook and Apps are capable of running this one, Catalina

Best of luck