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Hello, The Android P beta program released for Nokia 7 Plus is just a Developer Preview which means this beta update is meant for developers so that they can optimize their apps for new Android P. This year Google picked a handful of devices like Nokia 7 Plus so that it would be easy for the developers to work and they don't have to own a Pixel device just to test their apps for Android P. Also Android P is still in its developmental stage, many things are still to be changed and added to it which will still require more than 2 months of time to complete. In fact Google releases update for all the other Android devices including Nokia 7 Plus only after it has tested everything and completed all its developmental stage. So, at the end this Beta update(Developer Preview) for Nokia 7 Plus is not meant for general people and there will be numerous amounts of bugs in it if you are thinking to use it to complete your day to day work. In short, the Developer Preview launched for Nokia 7 Plus is pretty different from Nokia Beta Labs. So the beta update for us non developer users will be available after the final release of Android P. Thank you.
Hello, The Developer Preview launched for Nokia 7 Plus and the Nokia Beta Labs are two completely different things. For detailed answer check this link where I answered a similar question to yours. Thank you.