Still possible to override iSight webcam LED for iMac's and Macbook Pro's 2019 & 2020 & on?
From a practical stance, macOS now blocks all apps from the camera in software so you can easily know all apps that could even request access to the microphone or camera. 

In 2009 the firmware of the hardwired cameras was secured with encryption. I haven’t seen a credible report that this is broken, but depending on your threat model, you might close the lid if you can’t trust Apple to secure things. 


Does a newer MacBook&#39;s camera light need to be activated when the camera turns on?


Whether you trust the LED auto-functions and cannot fail as an intrinsic part of the operation would need to trust someone who can forensically examine the hardware (likely destroying it to be certain how it works) and assuming all are made the same. 

I think you the camera is the least revealing or worrisome part, but it’s fine to question and learn even if it’s a small risk or no risk or you have easy mitigation options. 

Also, all Mac cameras are hardwired. Just the security is far better hardware wire since 2009 and software side many steps better but with SIP and Catalina it’s really a hardened target for the software to get compromised.