Sunny Al
In the thread regarding warranty coverage on your new Beemer, I politely suggested that you need to read the details of the warranty coverage on your car. Those details are in your glove compartment, along with other documentation.
This thread leads me to a similar suggestion.
You REALLY need to read the Owner’s Manual that came with the car in order to get the authoritative word on this octane issue.
If the manual states, “91 octane gas required”, I think that is quite unambiguous.
If it states, “91 octane gas recommended”, that is a horse of a different color. In that case, you have been given an assurance by the manufacturer that your engine won’t be damaged if you use lower octane fuel.
Of course, your power output (and likely, your gas mileage) will be decreased with the use of lower octane gas, but if the manufacturer gives you an assurance that no engine damage will result, then that should give you some peace of mind regarding use of lower octane gas.
Please read the Owner’s Manual, the Maintenance Schedule, and the Warranty booklet that were provided by BMW if you want to derive the best use from your new car!