Sony has their own software for using your mirrorless camera as a webcam, whether APS-C or Full-Frame. But the quality is inevitably lesser to an HDMI adapter. A version for MacOS is being developped, according to their website

It's called "Imaging Edge Webcam" : https://support.d-imaging.sony.co.jp/app/webcam/en/

I'm personally using an A7ii with a Tamron 28-75 for Canon EF, and it works much better resolution and quality wise with the HDMI, just because of the limitation to 1024x768 of the USB camera mode, which was really meant for tethering. Coupled with a 4$ phantom battery, it's awesome! I can get a clear image in the very low light conditions of my room at night, too. No need to turn the lights on, even :)

Is that using the tethering feed? I wasn't wild about the quality, ymmv, seemed lower res than my webcam. Here's how to do it using gphoto2 in Linux: https://news.ycombinator.com/item?id=23407365

Yeah, it uses the tethering feed, and I had to tweak some setting in CamTwist to get 1080p.

Starting to think some kind of capture card might be worth the investment though.

I ended up buying the $10 1080p USB capture card recommended in a sibling post, and it's much better than what I got out of the tethering feed.