@yiv xiao Thanks for posting in our Q&A.
Xiaomi 12 is a supported android device to be enrolled to Intune. Here I have some suggestions you can try to see if it can fix the issue:
1. Check if there exist any restrictions in Intune portal.
Intune portal > Devices > Enrollment > Device platform restriction
2. Make sure that the user you used to enroll the device has an Intune license.
3. Check if any work profile existing on this device. Remove it and try again:
a. Go to Settings->Passwords & Accounts
b. Find Work Tab
c. Remove Work Profile and enroll again.
4. Make sure the device is not listed in Entra ID portal and Intune portal. Then reset the device if possible and do the re-enroll.
Hope the above suggestions can help.
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