Hello, OliverPopeItsHandled.
Thanks for posting in Apple Support Communities. We understand that you're experience decreased battery runtime after updating to iOS 14.6.
You mentioned that one scenario where this occurs is while listening to music. Is the music downloaded on your device or streaming?
Keep in mind, low- or high-temperature conditions might cause the device to change its behavior to regulate its temperature:
Keeping iPhone, iPad, and iPod touch within acceptable operating temperatures - Apple Support
To better understand what's going on with your battery life, go to Settings > Battery. When that page loads, scroll down to the 'Battery Usage By App' section to see which apps are the most active. You can also 'Show Activity' by tapping those apps to find out why (on screen, background activity, etc.)
You can also find suggestions that improve battery life on this page.
Check for any app updates: Update apps or use automatic downloads - Apple Support
We also recommend these tips: Batteries - Maximizing Performance - Apple
Let us know if this helps! Take care.