I reported a similar issue to Zoom on April 9, 2020 and did not receive a reply. I did not test to see if it has been fixed since.
The issue: While watching Zoom webinars on Mac, clicking on Audio Settings auto-activated the mic for testing audio levels. However, Zoom forgot to deactivate it upon leaving the settings. For the rest of the webinar, the input device stayed activated in the background (as evidenced by OverSight and Micro Snitch). I could not find a way to deactivate it.
The issue: While watching Zoom webinars on Mac, clicking on Audio Settings auto-activated the mic for testing audio levels. However, Zoom forgot to deactivate it upon leaving the settings. For the rest of the webinar, the input device stayed activated in the background (as evidenced by OverSight and Micro Snitch). I could not find a way to deactivate it.
This issue is similar to one that affected Shazam: "Shazam Keeps Your Mac’s Microphone Always On, Even When You Turn It Off" https://www.vice.com/en_us/article/8q8ee3/shazam-keeps-your-....