> Depends on your view of lightweight

Basically, what I care is that as I’m running the game, the system is consuming as few resources as possible. It’s an outdated machine, so every bit matters.

> probably XFCE Ubuntu (Xubuntu)

Thank you. Will check it out.

I'm a big fan of Linux. My small business and personal life run on it. You can download XFCE/Ubuntu spin at https://xubuntu.org/download/. If you develop on your Apple system, it will be pretty similar except

- App Installation via repositories is more common than single program installs. No DMG files. There is a similar concept to DMG with "snap" installs. Steam should probably be installed via a snap. You trust the producer (Valve). But most software and security should come through repos (in CLI, sudo apt update && sudo apt upgrade)

- Home directory is /home/<username>

Much of the rest is similar -- Apple's BSD and Linux share a common Unix design progenitor.

Linux is way open to rewipe, just pay attention that you don't lose files. My first day on Linux in the mid 2000s, I somehow overwrite the file system allocation table with the content of an MP3. It was recoverable!

Good luck, and have fun!