Could it be, that in twrp you mount system partition complete without to cross the option "mount system read-write only"?
On the other hand there is a possibility to discuss with the developer und contributer of twrp direct in this thread...
After Clean install in the morning all work like a charm.
For AI button: look giantons post #310. Works for me.
https://xiaomi.eu/community/threads/9-8-22.51929/post-500293
All users of Mi9 have this problem. Xiaomi Inc. decided to develop his phone with button and rom without OK-Google command (since yet ...)
Many hate this, waiting for patch or magisk modul etc ...
sure
https://androidfilehost.com/?fid=6006931924117942286
Is from XDA Thread
https://forum.xda-developers.com/Mi-9/development/recovery-unofficial-twrp-xiaomi-mi-9-t3905825
Same as me, same twrp, same dirty procedur. Other user recommend "clean" flash of 9.8.22. I will try this with twrp 3.3.1-39, wether i get a little time.
Edit: Go Back to twrp a flash magisk again.
Do you have try to flash magisk from internal partition too?
And wether the report ist again "cannot mount system", -
Edit: do you have try to unmount system in twrp, and after that flash magisk from internal?
See linked post from matata86 and andere...
Mi9, twrp 3.3.1-39,
after dirty flash 9.8.22 over 9.8.15 there is a force close of "battery & performance" after every boot dircetly after activation of sim Report (2x)
No magisk, no FrancoKM, no greenyfy, no lkt.
Ah, you want to hold Android 9. Yes brandnew mauronofrio twrp is the correct one.
(as new option versus 3.3.1-37, you don't need to flash it on phone anymore, you can flash in PC "throught" it virtually - even magisk etc, hold the original stock recovery untouched)
If you uncertain with "new"...
Yes, because your described work sequence is not correct.
My way is (with USB stick, without fastboot push command):
1. Flash newest 3.3.1- 39 mauronofrio twrp (over pc fastboot)
2. Boot in twrp, disconnect from PC, wipe, format partition
3. Connect USB OTG to Mi9 with newest Xiaomi rom...