Pysonix supported Linux at launch. Then, a few months after Epic Games, inc. bought the studio, this message was posted on their website and support was dropped.

The macOS and Linux (SteamOS) versions will no longer be updated or supported after the final patch. You will still be able to download and install these versions, but some features will not function as expected.

http://archive.is/1whPg

Refunds were made available if you owned a Mac or Linux version.

Hi everyone, if you are playing RL on macOS or Linux and are interested in a refund, please contact our Customer Care team here: https://support.rocketleague.com/

http://archive.is/WnVDe