Hello Doc_Theo,
It sounds like you've been unable to permanently remove a Bluetooth accessory from your iPhone 11, even though you don't have that accessory in your possession and have chosen Forget This Device. You've come to the right place for help with this. I'm happy to provide you with some guidance on removing that device from your Bluetooth list.
When you go to Settings > Bluetooth, and tap on the little "i" next to the device name for those Powerbeats, do you see a Disconnect option? If so, try tapping on that first and then selecting Forget This Device. Next, power your iPhone off and then back on. If you continue to see that device listed after the restart, update your iPhone to iOS 13.2.3 if you aren't currently running that version. Keeping your iPhone up to date helps it run as smoothly as possible, and can sometimes solve software-related issues like the one you're experiencing.
Thanks for using Apple Support Communities.
Take care.