Apple Watch activity alerts too loud on headphones

Since the update of my Watch to iOS 26 the notification of an Activity (like the 1 km notification during a walk) are way too loud over a headphone.

I don’t get any sound notifications if I don’t use a headphone. But if I listen to music the notifications will pop on my headphone, but the volume is soooo much louder than my music. It hurts my ears.

If I toggle the sound buttons during a notification, the next ones will be softer. But with a next Activity, it’s back to being painfully loud.