Xiaomi is amongst the manufacturers which allow users to switch between different MIUI ROMs without worrying much about the warranty, users can upgrade/downgrade MIUI ROMs on their devices using Fastboot and Updater method. At Google I/O, Google announced rollback protection feature, and now Xiaomi has announced that it will no longer allow Redmi Note 5 Pro/ Redmi Note 5 users to downgrade MIUI Stable and Beta ROM after you have updated to MIUI 10 Public ROM 8.7.5 or later.
A post by an admin on MIUI Forum says,
To maintain system stability and ensure the security of the device, we have introduced a mechanism of anti-rollback. After you have updated to MIUI 10 Public ROM 8.7.5 or ROM afterwards, you can not downgrade your ROM to previous Stable ROM and Beta ROM. If you have already updated your device to MIUI 10 Global Beta ROM 8.7.5 or ROM afterwards, please don’t try to downgrade the ROM of your device. Otherwise, your device will be bricked, which may also affect your device stability.
If you want to test ROM prior to 8.7.5, you can remain on the previous ROM, which will not affect your using of the device.
MIUI Forum admin has nowhere mentioned the reason behind this, but a Super moderator has provided the following reason in his reply,
This flew under our radar back at I/O, but it’s big news. On compatible devices, the new Verified Boot changes in Android 8.0 Oreo will prevent a device from booting should it be rolled back to an earlier firmware. The new feature is called Rollback Protection. So if your phone is flashed with older software, you (and your data) are protected from whatever potential security vulnerabilities may have been present in earlier versions.
For 99% of users, the new Rollback Protection is great news. If a phone is lost or stolen, it further decreases the number of potential attacks which could be used to gain access, providing better safety for your data.
The decision is going to affect user experience as Xiaomi doesn’t have a good record of providing bug-free update, and in fact last couple of months the company suspended updates multiple times for various devices including Redmi Note 5 Pro and Mi A1. The decision will make the current situation even worse if Xiaomi doesn’t improve on releasing bug-free updates. We advise our readers to not update their devices before getting feedback about the update as they can’t downgrade ROM anymore in case the update is buggy.