I have mi 9 too. I would flash global with mi flash, that's could work?I did it before with my mi9 without any problems.
Which device do you have? If your device does not have the ARB you can go back anytime you want. Maybe better flash android 9 with fastboot rom and mi flash tool. Flash the android 9 version rom with twrp might work but fastboot rom is more secure in these cases in my opinion.