Tested on Windows now. “Treat as linear” also has no effect there.
There is a difference between Windows and Mac though. This screenshot has the same settings as the first one from Mac (Default (not checked)): Linear Workflow turned on, Treat as Linear turned off, no manual gamma adjustment of the texture. It’s clear this one has been de-gammaed before rendering, while the Mac version has not.
They should probably work the same on both platforms 