I flashed 2 different mi8's but haven't noticed any issue regarding mic. or lag. Everything is perfect.
They are both originally from China, one 64gb and the other 128gb. Flashed them this way (commands not exact but to clearify the steps I used)
1. Fastboot flash recovery lineageos19.1-recovery.IMG
2. Boot into recovery and wipe everything (data, system, cache).
3. adb sideload fw-global (this one:
https://xiaomifirmwareupdater.com/firmware/dipper/stable/V12.0.3.0.QEAMIXM/)
4. adb sideload lineageos19.1
5. adb sideload mindthegapps
6. Reboot
7. Profit?
I first used twrp to flash but that didn't go well. Mindthegapps would constantly crash and ota update would boot loop. With lineageos recovery everything is great.