I’m going to be the pragmatist and suggest that you treat any mic and/or camera as live and avoid discussions in its vicinity that would lead to embarrassment. I realize that isn’t helpful to your original question, but still a little self-control shouldn’t be dismissed.
As for the actual problem, I think an “on the air” indicator that was controlled by the fact the software in use was able to hear/see you would be helpful… but I don’t use the technologies so don’t know how possible that would be to build. Ideally, if such an indication were wired into the mic and camera that would be the most fool-proof. Failing that, it would probably need to be built into the OS or a driver so that it worked with any software that might gain access to an input.
Windows Powertoys has an up an coming feature (still in alpha I think) to allow you to use a hot key to control the camera and mic. https://github.com/microsoft/PowerToys/wiki/Video-Conference-Mute-Overview