What is the correct Mac display profile for Premiere? Should I always turn on Color Management?

My Hi-8 Sony camcorder was designed to be played back on broadcast compliant hardware (a TV) not an iMac using Quicktime. My Canon T3i and your Sony A7S II both have an HDMI cable to connect to your TV. No camera or camcorder was designed for playback on an iMac using Quicktime or OBS studio. That is not to say it will not look correct by doing it that way. Having said that what does the video look like when the camera is connected to your TV ?  Keep in mind if you upload to social media you should be more concerned with what your rendered video looks like on a Windows 10 PC at your local library. The video below might be helpful.

We would need to know what the monitor is set to, and what ColorSync is set to. As it is doing something whether you've touched it or not.

Neil

The biggest issue is the OS ... is your OS running a newer Mac OS that has ColorSync?

For some bizarre reason, Apple decided to only partially comply with the Rec.709 standards. Notably, they only apply one of the two required transforms in the standard. They apply the camera transform function, but not the display transform.

Instead of the proper display transform, they apply what they call "sRGB gamma" ... which is effectively around 1.96 or 1.95. And has never, ever been part of any broadcast or other pro use standard.

What is the monitor set to for color space? What is the OS set to for color space? Have you done any calibration using a software/puck setup like the Xrite i1 Display Pro?

Neil