Thanks to Proton work, VMProtect hurdle has been passed and the new issue is in regards to the challenge packets that the game sends at start.
Nice. But with that kind of money they can make a proper Linux client already.
You've got to consider how tiny of a market share Linux has in the "adult" world, then remember Roblox is mainly played by kids. How many kids do you think are using Linux? To Roblox, porting to Linux would be absolutely worthless. Not saying I don't wish it was on Linux too, but it really does seem completely pointless for them.
Incidentally, minecraft runs fine on Linux.
but aren't they trying to retire the java version?
I'm not a very regular player, but from what I understand, the Java version is the most popular by the "enthusiast" community. At least the people I know that are very into the game still use Java for modding purposes and more extensive server options (also because of mods).
Yep, if you run a Minecraft server you are most likely using the Java version with a wrapper such as Spigot (or one of its forks)
Hard to say for sure without being inside the org, but from the outside that doesn't really seem to be the case to me. Most gameplay features appear first in snapshot releases of Java edition.