I haven't played it since the buyout either, but I'm told it works perfectly with Proton.
You can no longer use Proton on a Mac (unless you have one of the few models supported by Asahi)
Yes, running the windows version of Rocket League might be possible. But that's not what I bought.
You can no longer use Proton on a Mac (unless you have one of the few models supported by Asahi)