If you are using APFS Case Sensitive File system and trying to use Steam, it will flicker & silently fail or show the following error message:
steam requires that '~/library/application support/steam/steam.appbundle/steam/contents/macos' be on a case-insensitive filesystem.
To fix the issue, follow the instruction here.
$ brew cask install steam
$ diskutil apfs addVolume disk1 APFS Steam
$ mv /Applications/Steam.app /Volumes/Steam/Steam.app
$ ln -s /Volumes/Steam/Steam.app /Applications/Steam.app
$ mv ~/Library/Application\ Support/Steam /Volumes/Steam/Library
$ ln -s /Volumes/Steam/Library ~/Library/Application\ Support/Steam
Then start Steam as normal.