I pay for YouTube premium for my family and there haven’t been any injected ads at all. Only the ones that the video themselves have in, which are also very annoying.
I can’t speak for the future, but I’ve had this for probably 5 years and I haven’t seen a single ad, only the videos that I’ve asked to see.
It works amazingly well provided a video's been out for at least a half hour or so. It also has the option to skip the "like and subscribe" parts too.
I also tried the https://dearrow.ajay.app/ extension to replace clickbait titles, but decided I'd rather know when a channel/video is too clickbait-y so I can block/unsubscribe.
I can’t speak for the future, but I’ve had this for probably 5 years and I haven’t seen a single ad, only the videos that I’ve asked to see.