I discovered that brave for iOS has a playlist button which downloads YouTube videos and stores them on your device, allowing PiP and offline playback without ads. I wonder why more apps don't do this as they have an open license based off a Mozilla iOS backend. They found a way to get Apple to accept it and their CEO has even posted HERE about it defending their technique as valid. Essentially, it triggers only after loading the video inside the regular YouTube website, like a reader button that works across any video content (not just YouTube).