edit: Better watch this review first. You'll get better support from Atomos but it might not be worth the big price premium.
Also available directly from digiDirect for $113.90 C&C. Thanks to RichardL for the eBay tip!
Move over Elgato CamLink, we finally have a big-name competitor that's far cheaper.
Atomos, the famous Melbourne company who makes reasonably high-end video capture gear, has released a really low-cost UVC USB HDMI capture dongle.
It allows any HDMI device to appear as a webcam, so you can use your new A7C to Zoom at 35/1.4 in full HD (the Imaging Edge webcam feature is a paltry 1024x576). Or you can use it to stream with OBS, or anything that can use a webcam.
It can accept up to 4K30 and 1080p60.
$107.20 Delivered from their eBay store with eBay Plus and code 'PLUSBF20'