Anyone know how to fix IOS 14.3 iPad problem with messaging?

If you are not receiving iMessages on the iPad, go to Settings>Messages>and see if iMessage still shows activated. You many need to check the troubleshooting steps in this support document. If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support

Since you are saying iPad, one has to assume that you are referring to iMessages. What happens when you try to send a message? If you are not referring to iMessage and you have an iPhone, have you checked the settings in Text Message forwarding on the iPhone?

What happens when you try to sign in? Are you seeing an error? If so, have you followed all of the steps in the support document? The final step is to contact Apple Support and provides a link.

Use the Contact Support link at the top of the page here to contact Apple Support for assistance.