Welcome to Android Central! I agree that it's a nuisance to have Ringtone and Notification volumes tied together, but this has actually been the case for "vanilla" Android for a while (i.e., that's how it's been on Pixel and Nexus phones for as long as I can remember). Other manufacturers may tweak the system settings so that you do have separate control, but that's up to the manufacturer. If your phone doesn't have this option, then you'd have to look into a 3rd party app -- however, the main one I found on the web (Volume Butler) isn't available through the Play Store, so there is a bit of risk if you install the apk.
The workaround for me is to change the notification tone to something quiet and/or brief. If none of the preinstalled tones fit that criteria, then you can always download one from the web, copy it to the /Notifications directory, and use that.