Meshel02 Said:
"music player on lock screen: Do you know why that pops up when the app is not even installed?“
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Caches being the Culprit:
Music is an app that is built into the iOS. So, it’s not going to be deletable by the user. But, sometimes apps mysteriously just disappear. If you want the Music app to not show up, then disable it in Screen Time. If this window will not close, however. then the Music app likely went missing, somehow. It’s all caches that have been misconfigured.
Resetting to Factory Settings:
So, is the Music app still here? If so, I’d say reset your iPhone to factory settings, backing up fist (if an available option). So, if this still resides, there perform as instructed here, including the backup: What to do Before you Sell, Give Away, or Trade in your iPhone, iPad, or iPod touch - Apple Support