I can launch the
Messages app on Catalina and send an SMS to anyone on my iCloud or Gmail contact lists, which gives me the convenience of touch typing replies, as well as seeing attachments on a large screen—except for one contact.
This one contact, with whom I communicate often, uses an Android mobile phone. I had understood that so long as I am using a recent enough iOS version (it's 14.1) and a recent enough macOS (10.15.7), and am logged into both using the same Apple ID, I should be able to message anyone on my contacts list using the Mac's keyboard, regardless of the mobile OS of the person on the other side, indeed even if the other person uses only a very basic phone device.
When I enter this recipient's name in
Messages, I only get a few older messages. When I receive messages from this one individual, I can only see them on iOS, not through macOS.
Why are some message-recipients reachable through iOS but not macOS?
In case it matters, this one contact used to use an iPhone, but moved to Android. Yet even when using iOS, I was receiving "green", not "blue", message bubbles, signaling that the messages are sent/received through the phone company's networks, not through iCloud.