My 11-month old phone “only” has Android 7.0 and I can’t find this ability to change notifications and custom sounds anywhere.
Given that I only change my phone every three years, I’m now doomed to hate this notification sound for a very long time.
Doesn’t seem much to ask to add in to the app the ability to change the sound back to the system’s default one…
If your phone doesn’t have the upgrade already it likely will in the next couple of months. 12 months is practically new. Most manufacturers these days have 2-3 year update support (samsung is 2 major updates, which is roughly 2 years in practice).
It was introduced in 7, what do you see if you press and hold the notification?
I have a feeling Sony may have hidden it away with their own UI if neither press/hold or swipe/gear work.
OK, my phone got an upgrade from 7.1.1 to Android 8.0.0 and now I see the 9 notification categories. However according to official statistics Android 8 accounts for 1.1% of all Android devices, and even Android 7 accounts for only 28.5%.
Bear in mind that’s a percentage over over 1 billion devices 
So not a small number, even at 1.1% 
It’ll also increase rapidly. Samsung are still such a large percentage of devices that when they update you gain 20% overnight (potentially 50%, but lots of people never update even though one is available. Similar to Windows, were we still have to support XP… people don’t like change).
Supporting XP 
Not my choice… But people with money to spend haven’t upgraded yet and don’t plan to… and I like money.
Then there’s the many hours trying to support legacy opengl 2.0… (Dropping support for 1.1 was hard enough… people run some seriously old crap out there).
Just a heads up for those suddenly getting bombarded with loud cash register sounds again: A recent update made notification settings more granular, but also reset all notification categories to playing sounds again. You now need to go to notification settings as before, and then for each category of notification (e.g. account debits, account credits, etc) tap on that category and choose to “display silently” from there.