The latest version of iOS is rolling out, though it’s only available for iPhone 12, iPhone 12 Pro, iPhone 12 Pro Max and iPhone 12 mini.
According to Apple’s release notes, iOS 14.2.1 resolves these issues: Some MMS messages may not be received; Made for iPhone hearing devices could have sound quality issues when listening to audio from iPhone; Lock Screen could become unresponsive on iPhone 12 mini.
Some iPhone 12 users have reported problems with SMS messages not coming through in group threads or notifications not popping up for messages they did receive. Others have flagged issues with sound quality on paired Made for iPhone hearing devices, while complaints have emerged regarding lock screen responsiveness on iPhone 12 mini. If any of those problems have been affected you, updating to iOS 14.2.1 should take care of them.