At a glance
Outlast has a Mac version: Steam sells it for macOS. The Mac requirements list only Intel: on Apple Silicon Rosetta 2 runs it, and old Mac versions sometimes do not start on current macOS. Try it in Steam for Mac first.
Outlast came out on Steam on 4 September 2013, made by Red Barrels.
What your Mac needs
The Mac requirements list only Intel.
Minimum macOS in the Steam requirements: 10.9.
Steam requirements list at least 4 GB of memory for Outlast.
Allow about 5 GB of disk space for the Mac version.
How to play
Open Steam for Mac and install Outlast as usual.
If the Mac version will not start, you can install the Windows version through Uncork: download Uncork, sign in to Steam and install Outlast from there (5 GB). We have not tested it ourselves.
The Windows version through Uncork needs a Mac with Apple Silicon (M1 or newer).
Outlast uses DirectX 9.0c: Uncork renders it with its built-in graphics.