I’m curious to know what you’ve been using that gets outright rejected. I’ll often use copyrighted music and usually I am told that “the copyright holders are allowing you to use it” but that just means I can’t monetise the video, and I’m light years away from being able to monetise videos anyway. Sometimes it will mean my video is blocked “in certain territories” (usually Russia, etc.) and on very rare occasions the copyright holders don’t allow their music to be used, but I think that’s only happened twice in all the years I’ve been shoving videos on YouTube.