My Safari extension StopTheMadness has a ton of features, which is great! Except when it's not. One downside to all those features is that an individual feature can get overlooked or forgotten. One such feature is "Show video controls", included with StopTheMadness for 2 years on macOS and since the beginning (September) on iOS. When this website option is enabled, StopTheMadness replaces the web site's custom video controls with Safari's native video controls, including picture-in-picture, full screen, AirPlay, and the timeline scrubber! It works not only on YouTube but on almost every site on the web with custom video controls.
Here's a little iOS PiP tip that Apple doesn't explain very well. In the iOS Settings app, General, Picture in Picture, you can enable Start PiP Automatically. The explanation of the setting says, "When this is on, videos will continue playing in an overlay, even when you press the home button." What Apple doesn't say is that this setting applies only to full screen videos, not to inline videos. There's an HTML
<video> attribute playsinline that makes a video play on mobile in the web page instead of in full screen; embedded videos (and advertisements) are typically inline. If you want the setting Start PiP Automatically to work, you have to play the video in full screen (if it's not already PiP).
One More Thing: StopTheMadness can also stop video autoplay on all web sites, including YouTube!
Ok, Two More Things: There are some nasty web sites that can cause your background audio on iOS (such as in Music app) to pause when you visit the sites in Mobile Safari. The "Stop video autoplay" website option in StopTheMadness mostly stops this, thankfully. And for a few particularly devious sites that manage to get around my first line of defense, I brought a sledgehammer: the "Stop all audio and video" website option will totally silence a site and stop it from ever interfering with your background audio.