Currently, the macOS version of Portal 2 is 32-bit, which is no longer supported on modern macOS versions (since macOS Catalina).
As a result, it is impossible to run the game natively on newer Mac computers or macOS versions.
A 64-bit build compatible with Apple Silicon (ARM64) or at least x86-64 (Intel) would make it possible to play the game again on macOS, whether via Rosetta 2 or natively.