According to Harmonix, “As we continue to upgrade Rocket League with new technologies, it is no longer viable for us to maintain support for the macOS and Linux (SteamOS) platforms. As a result, the final patch for the macOS and Linux versions of the game will be in March. This update will disable online functionality (such as in-game purchases) for players on macOS and Linux.”
However, the developer notes that this only applies to online multiplayer. The game will continue to function just fine, except that it will be pretty much limited to offline play like Local Matches. Gamers who want to play with their friends will still be able to do so, except that it will be limited to local multiplayer with splitscreen play.
It is a pity that the game is losing its online multiplayer feature, so that’s something you’ll want to keep in mind come this March, especially if you take advantage of the feature quite a bit.