Psyonix announced its intention to remove support for the Linux and Mac versions of Rocket League. After some complaints from fans, the studio further explained the decision, and helped effected players claim refunds.

On Thursday, Jan. 23, Psyonix announced it will pull support for the macOS and Linux versions of Rocket League this March. After some frustrated comments from the Rocket League community, the developers launched a post on the games subreddit, explaining the refund process and offering new information on why the company decided to pull Mac and Linux support. Following some teething problems, Psyonix is now offering a streamlined method for attaining a refund via Steam:

• Go to the Steam Support website
• Select purchases
• Select Rocket League (you may need to select view complete purchasing history to see it)
• Select I would like a refund, then Id like to request a refund
• From the reason drop-down menu, select my issue isnt listed
• In notes, write please refund my Mac/Linux version of Rocket League, Psyonix will be discontinuing support

Despite the new process, many commentators in the thread were still unable to refund their copy, or described a long battle with Steam to make it happen. Despite Psyonixs advice, some players in the thread said they could only get the refund through a manual refund ticket rather than a Steam bot.
As for why Psyonix is shutting down the macOS and Linux version of Rocket League, the studio offered an explanation:
Rocket League is an evolving game, and part of that evolution is keeping our game client up to date with modern features. As part of that evolution, well be updating our Windows version from 32-bit to 64-bit later this year, as well as updating to DirectX 11 from DirectX 9.
There are multiple reasons for this change, but the primary one is that there are new types of content and features wed like to develop, but cannot support on DirectX 9. This means when we fully release DX11 on Windows, well no longer support DX9 as it will be incompatible with future content.
A representative from Psyonix explained that the developers would need to invest more into the macOS and Linux systems than before to keep those platforms up to date. Psyonix would also need to invest in frequent support for the two platforms as new systems could easily break on the DirectX 9 replacement pipelines on Mac and Linux.
Psyonix also said that macOS and Linux users combined account for only 0.3% of Rocket Leagues active player base. As such, the studio made the decision that these platforms arent worth supporting.
For players unable to successfully claim their refund, Psyonix recommends submitting a ticket to Valve. MacOS and Linux players interested in playing Rocket League before it goes offline have until March 2020 to do so.