This sounds very similar to an issue that occurs commonly with the iPhone 12 (and newer). It could be that there is an issue with your ambient light sensor. Your screen may not actually be off, but extremely dim.
The apple shows up normally because this shows at full display brightness regardless of settings. Once the phone boots your brightness settings would kick in (potentially auto brightness) and if there is an issue with the phone's ability to tell how bright the environment is, it may assume the surrounding area is dark and turn brightness down to minimum. See if you can see an image if you shine an image at the screen, or if you go into a dark room. [br]
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It may have been this issue was underlying, but the software update pushed it over the brink of failure, or the iOS update reset your brightness settings, etc... [br]
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If that's the case you'll need to [guide|113605|replace this receiver speaker and its attached flex cable|new_window=true]. You'll lose your Face ID functionality without some programming, or transplanting the flood illuminator, which is paired to your logic board, to the new flex.