Cannot mute media notifications

When I migrated my old phone to Fairphone 5 using Googles migration tool, all notifications produced the notification sound. This is definately not supposed to happen, as some notifications are updated regulary and pretty much ends up playing the notification without stop, while others should just be silent. Like watching a Youtube video in Chrome or just casting to a chrome cast.

For all the normal notifications I have manually muted what I want to mute. But in the cases with videos and Chromecast that option is disabled. It’s like Google disabled it because they would be too annoying with sound - but due to an internal error they are set to be unmuted.

Does anybody know how to mute those notifications?

Did you try muting it in the notification bar? Hold a long tap on the notification itself and you get the option to mute further notifications of the same kind.

That is exactly what I do, and all options are disabled for these notifications.