There is a bug in One UI 7 where switching off live notifications for the media player removes all media controls. No media player appears on the lock screen or in the pull-down notifications list if live notifications are off.
If you turn off live notifications for the media player, then the OS should revert to showing media controls as a standard notification, as it did in One UI 6.1.
Ah yes, my misunderstanding, sorry. It does appear in the full panel (double swipe down), but not in the notifications panel (single swipe down) as it used to in 6.1 (and as it does with live notifications enabled).