Abiraterone (Zytiga) is a first-generation ARSI. You usually have to take it with a steroid, which brings its own side-effects.

Enzalutamide (Xtandi) is one of the second-generation ARSIs (together with Darolutamide and Apalutamide, the so-called "-lutamides"). They sometimes have lower side-effects and are far more effective, including significantly longer overall survival, but obviously, everyone's medical situation is different and they may or may not be suitable for you.

So Abiraterone and Enzalutamide do play the same role (trying to prevent cancer cells from receiving testosterone signals), but they're not interchangeable. They're like a v.1 and v.2.

There is now generic Abiraterone available in the US much cheaper. And it is covered in the US by Medicare, which now has a $2000 per year cap on what men pay out of pocket for prescription drugs. It must be taken with prednisone, which is dirt cheap.