On the official Rocket League website, Psyonix revealed that it will be ending support for the game's Mac and Linux versions in March. Psyonix says it's making this decision to ensure Rocket League players have the "best experience possible." The move will also somehow make it easier for Psyonix to "[adapt] to use new technologies."
It's unclear how ending support for two prominent operating systems will help Psyonix (and its new owner, Epic Games) achieve either of those goals; particularly the former. If anything, ceasing support for macOS and Linux will lead to a lesser experience for each platform's respective players, not a better one.
As for the bit about "adapting" to new tech -- we have absolutely no idea what Psyonix is talking about there. If our readers know of any Rocket League-related technologies that work on Windows but not on macOS or Linux, please let us know in the comments. In the meantime, we'll be reaching out to the developer for clarification on this statement.
Regardless, it's unlikely that anyone or anything will change Psyonix or Epic's mind at this point. As such, if you'll be affected by this change, we recommend getting in as much Rocket League playtime as you can over the next couple of months.
To be clear, you'll still be able to access the game on macOS and Linux when the "final" patch drops in March, but "some features" may stop functioning. We assume online play will be one of them, as it relies on constant updates and bug fixes to work properly. However, offline play should still be possible, and your cosmetics won't be going anywhere.