Read all pages... Noticed a few irritated reactions especially from people that are convinced that BT 'never paired' etc etc etc. As published by others, BT did 'pair' in the past. You were able to pair older iPhones and IOS'es and older MBook's with older OS'es with each other; maybe it was never intended to work, it did work. And now it doesn't: "Pairing not supported". I miss the feature, other people miss it as well, all for our own reasons, so maybe apple should rethink their strategy, however that is up to them.
Shall we now get over that issue (or better: fact) and continue to respect each other's opinions and thoughts on this post?
Ref hotspot-not-connecting-to-MBPro with later OS: I did reset my phone internet settings, and yes, before connecting to my iPhone hotspot, I turned off the MBPro BT. My hotspot did connect to my MBPro. Better even, if I now switch on my BT again, the hotspot remains connected. After that, leaving BT on, I disconnected the hotspot, connected to my local wifi account, did some stuff on i'net and disconnected my local wifi, and re-connected to my hotspot again, still having BT 'on'. The hotspot connected and worked. I logged out from my account, logged back on, this all leaving BT on, and surprise surprise, I was still able to (re) connect with the iPhone-hotspot. Only when shutting down and restarting my MBPro I have to switch off the BT before reconnecting with the hotspot; as long as I do not shut down my MBPro I can (re)connect with hotspot, after switching on BT after first log-in to hotspot. Hope this contribution is useful to some.