The add i implemetation after a long research find a company who ad advertise to your apk or other files but just a preroll and fixed banner support without coding now, the rest is very difficult to implement maybe of less coding experience.
if Lubos or Someone here have time can look or contact there someone for help , to get Interstitial,Banner,Rewarded Video work.
it was very hard to find weeks long ,here is the company everyone can load free apk or other application with ads out different providers like admob are supported.
please read first there the Instructions and not all options are for free
Dont forget to deactivate requests location permissions from users In the ads example google admob link otherwise your app will be download less.