Mate, I don’t know you but this is my first bike with reverse gear, however, this is not my first bike on the heavy boys league.
With previous bikes (where no R G was available) I used to read the parking space and park in a way I could roll the motorcycle backwards in neutral and front brake control. Hell I still do this to this day on my Bagger and I have a reverse gear working but I rarely use it. Park upwards and then use the incline to roll backwards when you need to leave. I wish I could show you my steep and bending entrance to my garage.
You can launch a legal action but believe me when I tell you that before BMW launched the compensation scheme for the reverse gear issue, their top lawyers when through the pros and cons , their liabilities, etc and hence the offering.
I honestly don’t believe you will get far and I do believe you will be out of pocket and disappointed with the results. This is not a case of gross negligence from BMW, where you could have a case, this is an “optional feature” potential malfunction and they are working on a solution. Remember the adaptive headlight malarkey? That was indeed a safety issue, took almost a year and no compensation was offered as far as I am aware, just a like for like replacement free of charge.
I am not saying you should not stand up for yourself or what you believe is right, but I seriously doubt you will win this case.