You could have had great 2.0 cables that the older is tolerated. This most recent upgrade could have added a feature that requires a better hdmi cable. My Apple TVs have been rock solid both before and after the upgrade. No issues at all. A software bug won’t usually impact one device and not another if the devices are set up identically. You need to isolate the problem to the least amount of complexity. Does the Apple TV work as expected when connected directly to the tv? Then the problem is with what’s in between. If it doesn’t work when connected directly to the tv then get the latest and greatest hdmi cable. If the atv still doesn’t work then it’s probably the atv. Could be a bad port that the new os is exposing. Or get a new atv and upgrade and see if the problem happens or not. Thats more expensive than just trying a new cable but do what you feel is correct.
I use a unifi doorbell with the homebridge app. Works perfectly.