while ad blocking has grown in prevalence over the years, for something like youtube I'd figured it was more than counteracted by the shift to mobile / TV (where ad blocking is more complicated)
whatever the merits, this (and google's neutering of extensions in chrome) signals a fundamental attitude shift from ~10 years ago; they're more interested in squeezing margins out of their dominant platforms instead of growth
As for backdoors, they may exist if you rely on a third party but it's pretty hard to backdoor the relatively simple algorithms used in cryptography