Thank you both for the useful links. I have studied them carefully before I made this post.
Adaptive Charging is not so important to me. I usually watch out and limit my charging from 20-80%. From my experience in the past couple of years, it truly helps extending the battery life.
The thing I'm interested in is Adaptive Battery of which I cannot find any mention on the forum. Even though there are plenty of people stating that their phone got "better" after some time using it (which implies that Adaptive Battery is implemented)...
Regarding the high Phone idle drain; I just can't seem to pinpoint the source of the drain. I suppose it's the not so wonderfull 4G coverage here where I live....but I disable internet for 95% of time when not using the phone (including all night). I can't seem to find the option to disable 5g except the Preffered network setting...