That'd be nice if it actually applied, but Apple has already made exceptions for X among other large companies to allow them to play by different rules in the store. So I'm not holding my breath for any sort of punishment.
Examples:
X got a one letter App Store name that was previously against the rules (other devs need their app name to be at least 2 characters) (more info)
YouTube had been blocking iOS PiP background playback (not sure if they still do) and put that feature behind the YouTube Premium subscription. Background playback and PiP is part of iOS's system capabilities and the rule specifically says it's not allowed. See Apple's guidelines section 3.2.2 (ii) here. With this, one could make the argument that PiP would only support system supported video decoding, and YouTube uses DASH for higher resolution videos, but YouTube does offer video and audio streams that are natively supported by Apple as well so I don't hold much support for this argument.
“Background playback” is behind the premium paywall; NOBODY gets YouTube PIP support on iOS; such a shame.
I repeat, even if you pay for premium you simply can’t do PIP using the official app. You can however use a browser and use PIP that way I think (there used to be some weird workaround but I’m not sure if it still exists).
Edit: I was (happily) wrong!
I see now, they added it halfway though 2022 and I needed to go into settings and explicitly enable it. I’m a happy camper now! Thanks for the correction
If you don’t want to pay for premium, I recommend (and use) uYou+ as a sideloaded app. It has PiP capabilities w/o needing premium, along with a built-in video downloader, sponsorblock, and adblock.
Assuming it works the same way as on android you just start playing a video then switch out of the YouTube app without stopping playback. In fact I just read the Google help page "Using picture-in-picture on your mobile device" and it says exactly that for any mobile device and only goes into iPhone Vs android specific details when it comes to ensuring you've not turned off any default on settings that are required for it to work.
My initial experience is that it was missing, then tested, then removed again.
Since you don’t have premium and can still use the feature on iOS, that means they were forced to make it available in general to iOS users. It was off by default for me though, so maybe they made it work but just didn’t turn it on by default?
Someone else above was saying that Apple has rules about this, and another poster was saying that on Android you need premium for PIP. So maybe iOS did without it for years and then they were forced to add it for all iOS users regardless of the premium sub.
Not on googles phones, pixels have a single good feature, call screening, if that wasn't so necessary for my mental health these days i'd go back to samsung in a heartbeat.
You can still play youtube through a browser like firefox and get working pip without paying for premium but if you want to use the official app its locked behind a paywall.