My HTC 10 just got Oreo. I can no longer set discrete sounds for notifications on most apps. It seems that any change globally changes the default sound. EX. I use 1 sound for incoming SMS, a different sound for FB Messenger, a 3rd sound for Whatsapp, etc., so that I know in advance which app is calling me. I then have the default sound for "everything else." FB Messenger app did allow me to change the sound only inside that app but the biggest problem is that SMS and "everything else" now seem incapable of having a discrete sound notification. Hopefully, I am missing an option. Each app displays "default notification sound" as the selection so I assume there is some ability to change that to "custom notification sound" ??
Update: I did discover that in Whatsapp, if you change the notification sound, the first option on the list is "default ringtone" which actually should say "default notification" since is selects the default system notification sound, not the default system ringtone." So, for me, the only real problem, is setting SMS as different from "everything else," although I do have several other apps that I would like to carve out, if possible.