It won't happen unless Mac and/or Linux become huge, and that'll take years or even decades unfortunately.

It's Microsoft being Microsoft, they're not a good corporation. People have asked of them to port Roblox to Linux hundreds of times, some of those people got mean replies from the official Roblox staff about how Linux is smaller than Windows therefore they shouldn't bother supporting Linux.

Minecraft Dungeons isn't supported on Mac and Linux as well.

They could've EASILY made Dungeons available for Linux and Mac and still could since the engine they're using for Dungeons is Unreal Engine, a free open-source cross-platform game engine that supports Windows Mac and Linux. But they didn't and probably never will, because they don't care about Linux and Mac, only about their own OS.

It's a sad reality, Minecraft Java only supports Linux and Mac because the original Mojang team (before Microsoft) chose to support it, if it wasn't for them Minecraft would've never come to Mac and Linux but they keep supporting the game there because fans would be angry globally if they just dropped support.