DISCLAIMER: Do this to access your game saves. Steam will not download missing compatibility but instead reinstall your games. Be sure to grab the saves beforehand.

Follow up, decided to tackle it on my lunch break. I had issues but the tutorial worked. All that tutorial does is help you mount NTFS on your Linux OS on startup automatically. Once you do that you're good to go.

The misnomer is adding the second library. The steam UI only lets you change the folder in the currently existing libraries (Settings -> Downloads -> Steam Library Folders is wrong). Instead try to install a game that you know is on that drive. When the game install prompt pulls up, for game install location select the dropdown and "Add new steam library", pull up your file explorer and set it to the `Steam` folder on your ntfs drive. After that it will search for common files for that game and install anything missing. It will also remove anything Windows specific. The process will also identify the rest of the games on the drive but will prompt for install when you try to play. I hope that helps!

Obviously your Proton matching mileage may vary per game!

That's a different problem, all together unfortunately. I think it is possible but I have not yet migrated that far. I am still in the "choosing a distro" stage (I'm enjoying Pop_OS so far but we'll see). I have read in some comments elsewhere that Steam will download the correct binaries if you can point to the library.

Your link is missing a `/` between `Proton` and `wiki` btw.