I'm running Resurrection Remix on my OnePlus 3, and am asking since it is based on LineageOS 16 and the ability to keep ringtone and notification volume separate has disappeared between the earlier Oreo build and now, to figure whether this is a problem with my ROM or depends on having the change ported back to LOS 16 from 15.
As an aside - this is one feature I wish Google hadn't removed, from around Lollipop onwards I think. I would rather have my phone ring loudly to alert me of a call, and at the same time for my notification volume to be discreet so that I don't get disturbed by loud volume of messenger and email notifications. I keep separate notification sounds for all my apps and even my email accounts so I can identify them without having to look at the phone.
As an aside - this is one feature I wish Google hadn't removed, from around Lollipop onwards I think. I would rather have my phone ring loudly to alert me of a call, and at the same time for my notification volume to be discreet so that I don't get disturbed by loud volume of messenger and email notifications. I keep separate notification sounds for all my apps and even my email accounts so I can identify them without having to look at the phone.