11.21r2 is the latest stable version.
11.25r1 is the latest beta version.
To install a beta version :
Steam users need to right click on x-plane in Steam interface, choose properties and activate beta program under the right tab.
Other users need to download x-plane installer, run it to update and tick the beta box at a given step.
Laminar Research recommends to only install beta versions on a second copy of x-plane, and only do so if you are ok to potentially deal with some bugs.
I am not sure Steam users can install a second copy of x-plane.
Other users can choose to install a second copy of x-plane through install/update process.
Finally, you should know that it can be a pain to bring x-plane back from a beta version to the latest stable version.