Given the first release of a game is named "Alpha", and another is named "Beta", it would be logical that the release following this one is named "Gamma".
This this the case?
No, there is no Gamma version nor do they call the final release this way. Here's the terminology for versions of a software/game:
You can read more here: https://en.wikipedia.org/wiki/Software_release_life_cycle
I have never heard anyone - in game development or software development in general - use the term "gamma version". After beta comes the "release" version.
However, the differences between "alpha", "beta" and "release" aren't very well-defined. The usual consensus is:
But different teams have different ideas about what to call "alpha", "beta" and "release". The difference between alpha and beta is hard to define because it is a matter of opinion which features are "core features" and which are not. And it is very common that games get released with known bugs or missing features because the developers ran out of time and/or money.