Specifically see from 19:00 onwards. Here, YQ states that a person who claims the sunnah has not been preserved is an innovator and this is not kufr. This is completely incorrect. To doubt in the preservation of the sunnah is kufr akbar and to doubt the kufr of the person who believes it is also kufr. It's the exact same as saying that Islam itself has not been preserved. This is not the same as doubting the authenticity of specific ahad narrations because that is neither kufr nor bidah. There is another video where he mentions that doubting the preservation of the sunnah is not mainstream Islam, implying it's still a part of Islam in general.
