My iPhone says connected to MacBook Pro. How do I stop this?

That is called Continuity Camera. It was introduced in iOS 16. See Continuity Camera: Use iPhone as a webcam for Mac - Apple Support

Instructions to turn off Continuity Camera are provided in that link.

I am getting this as well since yesterday every time I open my laptop. My phone and Mac have been synced and it's been seamless forever, so not sure why this would be happening all of a sudden. Anyone figure out how to make it stop? Google has been no help. I want them to stay synced, but not freeze up my phone like this every time I'm on my computer.

I too have been irritated by this problem. You can stop it by turning continuity camera off (see link in thread below) , but then you lose the continuity camera functionality which is quite useful. What i've found d is the irritating messages only appear when I have an app open that uses the camera - FaceTime, Zoom, etc. Close all those and the problem disappears.

iOS 18 and MacOS Sequoia brought something called iPhone Mirroring to Mac. Perhaps what you're seeing is tied to it --> iPhone Mirroring: Use your iPhone from your Mac - Apple Support