How to turn on MMS in Messages app on MacBook (Ventura 13.4.1)?

Hi klphilly,

It sounds like you're looking to sent SMS and MMS messages on your Mac using the Messages app. If so, check out the steps and requirements below from the article here: Set up iPhone to get SMS messages on Mac - Apple Support

"Important: To receive and send SMS and MMS messages on your Mac, your iPhone must have iOS 8.1 or later, and your iPhone and Mac must be signed in to iMessage using the same Apple ID. See the Apple Support article Use Continuity to connect your Mac, iPhone, iPad, and Apple Watch.

1. On your iPhone, go to Settings > Messages.
2. Tap Text Message Forwarding.
3. Note: If you don’t see Text Message Forwarding, make sure you’re signed in to iMessage using the same Apple ID on both your iPhone and your Mac.
4. Turn on your Mac in the list of devices.
5. If you’re not using two-factor authentication, a six-digit activation code appears on your Mac; enter this code on your iPhone, then tap Allow."

You can also find helpful information here: Forward SMS/MMS text messages from your iPhone to your Mac or iPad

Cheers.