iMessage turned off - If I have iMessage turned off - no reply from iMessage users

I've spent time with Apple support going through this. Basically if I have iMessage turned off on my iPhone Pro Max I don't receive SMS messages from people who have it turned on. This is new - ever since I got a MacBook Air last week. I've done all the resetting network settings, turning iMessage on and off, powering down and back up, etc etc etc. I have iOS 17.4.1. The last support person said that that is normal - if I don't have iMessage on I can't receive SMS from iMessage users. This essentially means that I have to have iMessage on, I don't have a choice. She said this is not new and that she would send me documentation to that effect. She said that the only way to change it is to de-register from iMessage. The documentation she sent me said no such thing. I am considering returning all my apple products unless....I am missing something?