I had same situation and fix that works for me is:
1. Flash stock fastboot MIUI 12 global (I'm not booting to system here)
2. Flash TWRP (still not booting to system)
3. Wipe vendor in TWRP
4. Flash MIUI 12 Stable from Xiaomi.eu (and finally first boot to new system)
Simple flashing stock fastboot rom always gives me broken NFC (greyed, turned on). Same with flashing any MIUI after custom rom was installed (like Lineage). I was struggling with pa-quartz-nfc-fix, different firmwares, wiping this and that, nothing worked. Only my method works for me when I want go back to MIUI.