Precisely. It is officially able to run Catalina, the most current one. You can update it directly from the apple store. But when Big Sur launches, you are likely going to be able to install it on your own through a patch. But it will not be accepted officially for the new system that should launch in a couple of months or less.
The official is what apple says they support. It will be easier to install (just click a button most of the time). The system is built to work on certain machines. In Big Sur's case, it works on 2013 macbook pro and later.
Read along with a quick look at all the Macs with macOS Big Sur compatibility. Big Sur includes new features like an all-new design, Control Center, more.
9to5mac.com
Here's a list of all compatible macs.
The patched system is basically like installing a new system in an old machine that apple doesn't want you to install on. It might run a bit laggy if you have less than 8Gb of ram and an old processor but should run just fine.
Another important thing is: Both will give you the exact same OS. And you can keep using Catalina for many years from now until Apple drops security updates. then you should probably move to the new one.