Please for information on how to control simple camera functions via local API. 

How to turn on/off Alarm Mode and Privacy Mode? Or at least set Home/Away?

It's not a normal 21st century device that calls itself "smart" without this simple functionality. 

Now I have to put another smart device (of course, NOT TP-Link) behind the camera so I can turn it on and off with scenes from Alexa.

Alexa integration is completely useless and unnecessary because it generally does not allow any functions (except Preview, which is also not stable at all).

Is there at least something similiar for the Tapo:

https://www.home-assistant.io/blog/2020/11/23/tplink-local-access/

P.S. Update Deco M9 too, I'm tired of seeing planned functionality of all your products, where it says "Will be added to future firmware". IoT mesh system without any basic functions... it's funny