You have to change the notication and sound settings in each app separately not like you could before ui 6 came along. It's every time consuming if you have loads of apps on your phone. Samsung never make things easy for you!
I usually had a different notification sound for sms and a general one for the rest of the apps. In One UI 6.1 , the option to change to a different notification sound for sms app,either google or Samsung messages,is gone now