Hello there!
First of all thanks again for the Magic DosBox, I wish I could rate it at 100 stars, this DosBox is just great 🙂
So, I tried to remap but it didn’t help…
I also tried to remap the built-in phone button (volume up), just for a test, and it did work.
So we can say that the remapping feature, in general, does work on my phone, it just doesn’t with the physical mouse.
Also, I noticed that during the process of remapping I can hold right-click forever, and this menu doesn’t show up.
Video here (sorry for my English):
https://1drv.ms/v/s!AlG9tVXDm9d3hKJjIjdwehHTvQEP9w?e=35m7JS
P.S. feel free to give up this troubleshooting if you feel that it’s not possible to fix that, I understand that fixing this kind of hardware/software issue is not always feasible…