The Mi Mix 3 was launched back in 2018. Xiaomi has been coy about its plans for a Mi Mix 4 release since then, but it appears that the company is now gearing up for that phone this year. And it could be joined by the Mi Note 11.
https://www.notebookcheck.net/Mi-Mix-4-and-Mi-Note-11-releases-potentially-on-the-cards-for-Xiaomi-this-year.514325.0.html