Just FYI, I bought a “new to me” 2015 MacBook Pro from my son’s friend and installed Gpredict on it. I use Gpredict to plan optical observing sessions (in the winter, I live on the Texas Gulf Coast in a swamp) but not to drive my observations. I used MacPorts and also installed X11/XQuartz - installation was pretty simple.
I load the CelesTrak orbits and also some others from the Observer community, so putting new orbits into Gpredict is easy, once you know how to do it.
There are ways that the application could work with the OS better, to control the size of controls, etc but it is quite usable.