iMessage settings for cellphone number

iMessage checklist:

iPhone and Mac both logged in to same Apple ID. Try logging off and logging on if necessary.

iPhone Settings => Messages shows iMessage as "on" (sometimes toggling this off and then on fixes some things)

iPhone Settings => Messages shows Send & Receive showing both phone number and email (Apple ID)

iPhone Settings => Messages shows Text Message Forwarding and your Mac is listed and shown as "on" there.

iPhone Settings => Messages shows Send as SMS "on" and MMS Messaging and Group Messaging both "on"

On the Mac: Messages => Preferences shows same and correct Apple ID and "You can be reached for messages at" indicates both phone number and Apple ID (email), and "start new conversations from" indicates the phone number.

You are not seeing your phone number there because the phone number has not been properly linked to the Apple ID. By going through each of the settings that I listed, most of which are on the iPhone, and some of which are on the Mac, you link them so that text messages can be seen on the Mac that come in to your phone. And you can send messages from your Mac that appear to be coming from your phone number.

You have to have an iPhone for this to work.

And those settings must all be set up as I indicated on both the iPhone and the Mac for it to work. Note my suggestions about logging out and in and toggling certain settings on and off.

When you have the settings up right, then the phone number simply APPEARS in your

Messages => Preferences => iMessage settings

I don't see a phone number in your screen shot so the settings on the phone and Mac have not been set up properly. This is called Text Message Forwarding and it has to be set up on both the iPhone and the Mac in the precise way that I indicated in my first post in reply to yours.