On an iPhone, listening to YouTube audio in the background usually requires a YouTube Premium subscription. Not everyone is willing to pay for this feature — and Premium is not available to users from Russia at all. But there is a way to enable background playback for free and without additional applications.
To do this:
Log in to YouTube via Safari and open the desired video.
Tap the "aA" icon to the left of the address bar. In the pop-up menu, select "Request Desktop Website".
Click on the play button.
When the video turns on, press the smartphone lock button. The audio will pause, but playback can be continued via the widget on the lock screen.
That's it: now you can put your smartphone in your pocket and listen to the video as a podcast.
If you want to listen to YouTube videos while using other apps, just swipe Safari from the bottom up. You can scroll through or stop playback via the Control Point or Dynamic Island.