Up until now, Samsung phones used the old-fashioned way of installing updates, locking the user out of the device for a substantial amount of time. However, this might change rather soon.
Seamless updates RSS
Samsung's Galaxy S21 series of devices do not support the Seamless update feature which Google added to Android a few years ago. This is despite the phones running Android 11 out of the box.
Google is going to require that all devices launching with Android 11 out of the box support the seamless updates feature. This was first introduced in Android 7.0 Nougat but OEMs have not adopted it.