Android 12 comes with some very good but tricky upgrades over the Android 11. It has been quite some time since Android allowed its users to install third-party app stores and also sideload individual APKs. However, the process was never easy or straight. Also the sideloaded applications would not receive updates automatically.
But that is certainly not the case with the new Android 12. Now, third party app stores can roll-out updates in batches and they will be automatically received by the user. Users will definitely have to grant third-party app stores the permission to manage internal storage but that would only be asked once. Users will not have to approve each time they install a new app. This is a great step by Google towards user-friendliness and ease-of-use.