The VoNR toggle was always available in Developer Settings. The problem with it of course is that none of the Canadian carriers have any plans to implement VoNR. I still don't have the update that enables VoLTE, so I've been using my Xiaomi Mix Fold 2. Enabling VoLTE on it was a simple as using the code in the dial app (although for some reason that only works on Rogers, not on Bell). It is also a lot lighter than the Vivo, although to be honest it is so light that I will probably end up losing my grip on it and dropping it one day.
It is a shame, the update has not come through for you yet, weird that Rocky got his and you are still waiting.
I hear you on that - so thin, sleek, and light.... one postivie with the Z Fold 4 (lots of cases to choose from), the Spigen Slim Armor Pro Pen Edition case, really feels good and has protection all around, to the point I feel pretty confident holding it and if it does fall, seems pretty tough to take some hits, lol, also
JerryRigEverything did a number on it so pretty durable, it will be cool to see him work on the Mix 2.... maybe there are some better cases out there you can try from
AliExpress that may help to protect the Mix 2 from some drops better than the one that comes with it, if you are OK with a little more size. I know I feel better about the Fold 4 with the case on it, than not.