I use this TWRP https://forum.xda-developers.com/xiaomi-mi-mix-2s/development/recovery-twrp-mix-2s-t3790922
Flashed it and installed magisk manager. TWRP said after flashing unable to mount storage, but the phone booted and it worked.
I think you have to disable screen lock to use this TWRP.
Flashed 9.13 in Polaris (mix 2s), clean install, data formated and no bugs ATM. Camera working, took several photos and a video to test. Magisk 17.1 installed and working. That's strange, because lot of people having bugs. I'm just testing things.