How to enable MMS Messaging in Messages app on MacBook Pro?

Ever since I upgraded to Big Sur the day before yesterday, I have not been able to send or receive photos via the Messages app on my MacBook Pro.

When I try, I get this:

I've been through all the Messages Preferences on my MacBook and don't see one that seems applicable (i.e., I don't find MMS mentioned anywhere).

MMS Messaging is enabled on my iPhone. And I have no trouble sending photos from my iPhone, but I don't receive those messages on my MacBook.

I'm using the same Apple ID on both devices.

Any ideas?

Thank you.