Looking at the schedule, Xiaomi will be releasing MIUI 12 in three batches, the first of which is by the end of June. The dates for the second and third batches were not announced, and this timetable applies only to China. According to XDA, the global release will be announced later.
But going in order of the current timetable, the first batch consists of these Xiaomi devices, including their Pro and Lite variants if they have any:
Mi 10Mi 9Redmi K30Redmi K20
These will be part of the second batch:
Mi Mix 3Mi Mix 2SMi Note 10 / CC9Mi Note 10 Pro / CC9 ProMi CC9 Meitu EditionMi 9 SEMi 8Redmi Note 8 ProRedmi Note 7
And finally, the third batch consists of:
Mi CC9eMi Note 3Mi MAX 3Mi 8Mi 8 SEMi Mix 2Mi 6XRedmi Note 8Redmi 8Redmi 8ARedmi 7Redmi 7ARedmi 6 ProRedmi 6Redmi 6ARedmi Note 5Redmi S2
It looks like devices that have been released two years ago are also getting MIUI 12. Of course, this, as mentioned, is the rollout for China. Hopefully international versions of the phones will be getting the new overlay as well. (Source: Weibo via XDA. Image: Android Authority)