Hi there Aldo_IceMan,
Can you clarify for us what appears to be different after updating to iOS 16.4 when playing music to your HomePod mini?
Also, to confirm, are you following the steps as seen below? We want to make sure we understand how you are playing music to your HomePod mini.
"Play audio on HomePod using Control Center
- To open Control Center on your iOS or iPadOS device, do one of the following:
- On iPhone with Face ID or on iPad: Swipe down from the top-right edge.
- On iPhone with a Home button: Swipe up from the bottom.
2. Tap the audio card, tap
, then select one or more HomePod speakers.
To play audio from other devices that support AirPlay 2, see the documentation for that device for details about selecting an audio destination."
That information, and more, can be found here: Play audio on HomePod using an iOS or iPadOS device - Apple Support
You could also see if you notice a difference restarting your iPhone, as it can help refresh the iOS and help resolve possible issues. If needed, this article shows how: Restart your iPhone - Apple Support
Take care.