Xiaomi has just unveiled the global roadmap for MIUI 12. The rollout will begin in June, and the software will make its way to the Redmi K20 and Mi 9 series first. Other devices will get the update later. Additionally, beta builds of MIUI 12 will be available to sideload starting next week.
https://www.notebookcheck.net/MIUI-12-global-rollout-to-commence-in-June-Redmi-K20-and-Mi-9-to-get-the-update-first.465983.0.html