What the Fix Addresses
Before the reported fix, a user could be using Mega888 and miss an alert that would otherwise have appeared. The update targets that behaviour during an active app session. It is separate from whether a notification arrives when the phone is locked or Mega888 is closed.
If you still miss alerts, note which app should have sent the notification and whether Mega888 was on screen when it happened. That is more useful than reporting only that “notifications are broken.”
Check the iPhone Settings Too
iPhone notification permissions and Focus settings can also affect which alerts appear. Check the notification settings for the app that sent the missing alert, then check whether a Focus mode was active. Apple allows notification settings to be changed by app and through Focus.
If alerts appear normally everywhere except during a Mega888 session, include that detail when describing the issue. If they are missing even when Mega888 is closed, the iOS 15.2.1 note may not describe the problem you are seeing.