Google added a useful "seamless updates" feature in Android 7.0 Nougat that greatly sped up the process of installing a software update. The feature required OEMs to create an "A/B partition setup" that would allow the OS to automatically create a copy of inactive partitions that could be updated in the background, with only a reboot being required to switch between them.
In a nutshell, this meant that your device would automatically create a second copy of the system and a few other partitions and install the new update on it. Then, the user would only have to restart their device to switch to the updated partition with the latest software thereby greatly speeding up the entire process of installing a software update. Google never made seamless updates a mandatory feature which is why we are yet to see the likes of Samsung and other OEMs implement this feature on their devices. One of the downsides of the feature was that it required an additional internal storage space which is perhaps why many OEMs have shied away from implementing it.
Nonetheless, Google is going to make it mandatory with the release of Android 11 that all devices ship with seamless updates support. As spotted on the AOSP Gerrit, a commit updates the Vendor Test Suite to reflect this change and it will be compulsory for all devices running Android 11 or higher to have a virtual A/B partition setup. The commit is yet to be merged, though that should happen before the final release of Android 11 to AOSP. Unless something changes, what this means is that the next flagship devices from all Android OEMs that launch in late 2020 or early 2021 with Android 11 will come with seamless updates feature as well.