Unfortunately, when you try running certain games on a mac, on a case sensistive HFS+ filesystem, you might hit a roadblock.
Steam itself will run fine.
Fortunately there is a solution by using OpenZFS. I won’t go into the details of installing ZFS on a mac as there is plenty of information out there. I simply use homebrew for that kind of thing. Refer to the OpenZFS Wiki, they have instructions on how to install using homebrew.
OpenZFS supports creating a pool inside a file, so this is what we are going to do.
mkfile -n 5g steam_disk.zfs zpool create -O casesensitivity=insensitive steam_pool /Users/$USER/steam_disk.zfs
Then you will get a shiny new volume with the required properties under /Volumes/steam_pool/. Fire up Steam, tell it to install there.
Enjoy, and don’t forget to read up on ZFS basics if you don’t know how to export and import a pool.
zpool export steam_pool zpool import -d /Users/$USER/ -a