The Xiaomi Mi A2 receives what could be one of its final updates
Xiaomi has rolled out the May 2021 security patch to the Mi A2, one of four Android One smartphones that the company released between 2017 and 2019. V188.8.131.52.QDIMIXM is the Mi A2's first update in two months, but it skips three version numbers from V184.108.40.206.QDIMIXM that Xiaomi released in March.
As usual, Xiaomi has only 'optimised system performance' and 'improved system security and stability', which is to say that it has upgraded the Mi A2's Android security patch. Xiaomi has not disclosed to which May patch that it has upgraded the Mi A2, so it could be 2021-05-01 or 2021-05-05. Regardless, you can read about what CVEs Google has addressed in the latest Android Security Bulletin.
Xiaomi is distributing V220.127.116.11.QDIMIXM as an over-the-air (OTA) download. According to Xiaomi Firmware Updater, the V18.104.22.168.QDIMIXM OTA is a 27.4 MB download. If your device has not received a notification to download the latest update, then you pull the OTA or recovery zip from Xiaomi's servers via Xiaomi Firmware Updater.
Xiaomi released the Mi A2 in July 2018 with promises to provide two OS updates and three years of security patch support. Hence, this month's update should only be followed by up to two more, if Xiaomi is feeling generous.