I appreciate the suggestions, and I thought we had a winner this time. It appeared to work at first - I set my notification volume at full, and ringer at the lowest level. Then I sent myself a text and it was loud, and called my phone and it was quiet. However, after the call, the notification volume was lowered to the call ringer level. I reset the volumes with the app (ringer quiet, notification loud) and called myself, again the notification vol dropped after the incoming call. So they seem to have the ability to separate the two volume levels, but Android wins in the end.
I use an automation app called
Automagic. I can set volumes with that, tho not ringer & notification separately. I can also react to incoming texts tho. I might try setting up a flow with that to increase the ringer/notification volume when I get a text, then reset it to the previous level, so calls won't be really loud. It's a long way around, but may be the only option if Google is so bent on making sure these volume levels are kept equal.