MMS Messaging
How Do I Enable MMS Messaging on MacBook PRO
MacBook Pro 15″, macOS 10.15
Question marked as
Welcome!
See these:
Forward SMS/MMS text messages from your iPhone to other devices - Apple Support
and
What is the difference between iMessage and SMS/MMS? - Apple Support
There is no separate enabling for MMS only. Enabling Text Forwarding as shown in the first article above enables both SMS and MMS IF your carrier supports it.
Without an iPhone, you can only text other Apple product users from your Mac computer.
If you have an iPhone and are having text forwarding issues, contact your carrier and see if they support MMS. Some do not.