Apple can't see the message receipt when texting. Was it hacked?

This needs to be divided into situations.

Messages sent by Apple's mobile phone don't show receipts. Maybe it wasn't hacked, maybe the receipt wasn't opened. If sending a read receipt is turned on, the machine may be blacked out if it does not receive a reminder of the read receipt.

It may also be that the other party's mobile phone has no signal for the time being, or it is turned off, or the other party has started the flight mode. When the other party's mobile phone has a signal, or turns it on or turns off the flight mode, the other party receives the message, and the user who sends the message will receive the notice that the other party has received it.