iOS update issues
Does apple have a known issue with passcodes not working after an iOS update?
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Passcode works well after the last update, unless you have forgotten it.
(< iOS 15.2) See this Apple article: If you forgot your iPhone passcode
If you forgot your iPhone passcode - Apple Support
(iOS 15.2 and newer) How to reset your iPhone, iPad, or iPod touch when you forgot your passcode
How to remove your iPhone, iPad, or iPod touch passcode without a computer - Apple Support