Sending text messages between Apple phones shows neither sent nor read. Is the number hacked?

No, it's just that the other party's read receipt option is turned off.

iMessage:

It is an instant messaging software launched by Apple, which can send short messages, videos and so on. It has high security. Different from the SMS/MMS service of operators, users only need the data support of WiFi or cellular data network to complete communication.

Sending and receiving method:

Select the email address and phone number you want others to use to send you messages, and then click Next.

Under Start a new conversation, select the email address or phone number you want to use to send information.

Please note: If you have set up other devices to use information, they will prompt you that the new device has set up the information function.