I just got an iphone 11 with bluetooth 5.0. I now can't consistently pair with the gen 2 bluetooth. I assume this has to do with lack of backwards compatibility. I also have a bluetooth audio car kit which is now what i use. Kind of annoying because I liked being able to answer calls on my steering wheel.
With the amount of money you spent on your phone, get your money's worth and make Apple work hard to solve this! Stop by the Apple store and online support again and again and again. You paid for the newest best phone they sell. If they can't solve these problems, raise hell. Keep escalating till they solve the problem!!! Don't take no for an answer!!! Or get a full refund!!!