Google seems to require the support of A/B partitions and thus installing an update on a separate partition in the background in Android 11. Manufacturers such as Samsung, Huawei and Oppo are not yet doing this.
XDA-Developers found a reference to the obligation to support A/B partitions in a commit in the public code of the Vendor Test Suite. A phone must pass those tests, otherwise manufacturers are not allowed to put Google services on the device.
Installing updates on a separate partition has been in Android for four years. Google Pixel phones and models from OnePlus, LG, Motorola, Asus and Sony, among others, support the feature, but phones from Samsung, Huawei and Oppo, among others, do not.
The feature has the advantage that users can continue to use the device while installing the update. On a reboot, the software then switches to the other partition. An added benefit is that if the update fails, users can go back to a working partition. Manufacturers who don’t support the feature let users install the update in recovery mode and then there is often no way to go back to the old software if the update fails.
If the obligation comes, it will apply to models that come with Android 11. Only devices that come out new must comply with the Vendor Test Suite; This does not apply to an upgrade to Android 11. That will probably happen from next fall. Then Samsung and Oppo will, among other things, switch to supporting partitions for updates. It is still unclear whether this also applies to Huawei. Due to the US government’s trade ban on US companies, current Huawei phones do not use Google services.
Diagram of operation updates on A/B partitions