HDMI projector connected to MacBook Pro stops displaying when file selection box is open.

There has been a recent thread where the affected users also were on Sonoma, and had this problem when mirroring the screen (to a projector or monitor) and using the Open or Save dialogs. This seems the same problem.

Apparently this is a bug only present in Sonoma (macOS 14): according to posts on this other thread, it does NOT happen in Ventura (macOS 13), nor does it happen in Sequoia (macOS 15).

so a quick solution, if your mac supports it, and you don't have any software impediment (like some old program that may not run on it), is to upgrade to Sequoia.

I will see if I can find that other thread. If I do, I will post a link here.

I’ve run into this exact issue on my MacBook Pro too—every time a file dialog pops up, the projector goes blank until I close it. Seems like a Sonoma quirk, and I haven’t found a fix either, just learned to work around it.

Here is the link to the thread I had in mind:

macOS Sonoma "Open File" menu results a "… - Apple Community