in your layout, only the main Deco and Deco 3 support guest network and work. Deco 4 can also broadcast guest network but no internet access.

The settings on the camera will be cleared after you reset it to factory default. a normal reset.

you can check the alert history under Antivirus page to see whether those have been blocked. better to email tp-link support with that screenshot to confirm.

yes, it can support LED lights.

generally speaking, the wireless channel should be the same as the main router. If the main router use channel 1, it should be also channel 1 on the extender. Have you tried on other devices? Does it...

if it's urgent, contact tp-link hotline support directly and they provide 24 hours service.