notification sounds are too loud

Greetings!

iPhone XS Max running iOS 13.6

When I receive notification (WhatsApp or iMessage message), I get very loud notification sound although I've set my notification sound volume to the minimum. When I get phonecall, the ringer sound is the volume I've set, but notifications doesn't seem to respect the volume value. Notifications are very loud.

It is annoyingly loud on minimum.

It is really loud even at the quietest volume setting while actual ringtones and message notifications are okey.

I am not sure what to do, I do not want to turn off notification sounds but it is not needed to hear them so annoyingly loud.

What is solution for this?

How do we change notification sound volume for individual apps?

Thank you.