Unable to add an external monitor to my MacBook Pro

birgers wrote:

so actually, it looks like my Macbook Pro only supports two monitors when the laptop is shut. it works now, but I thought it would be able to work with the laptop monitor also available ...

MacBook Pros with plain M3 chips only support two external monitors when the lid is closed. Apple's Technical Specifications clearly spell this out. (This is also consistent with the fact that no Mac with a base M1, M2, or M3 chip has ever been able to drive more than two displays – where built-in ones count against that total.)

MacBook Pro (14-inch, M3, Nov 2023) - Technical Specifications - Apple Support

When these Macs first came out, they only supported one external monitor. The line "Close the MacBook Pro lid to use a second external display with up to 5K resolution at 60Hz" only appeared in the Technical Specifications once Apple released macOS Sonoma 14.6. (All MacBooks with the plain M3 chip have the hardware to support a "lid closed" monitor, but only the Airs originally shipped with an OS that could take advantage of this hardware.)

Use dual monitors with your MacBook Air and MacBook Pro with M3 chip - Apple Support

so actually, it looks like my Macbook Pro only supports two monitors when the laptop is shut. it works now, but I thought it would be able to work with the laptop monitor also available ...

what model-year MacBook Pro?

what display, or a link to its specs?

I'm having this same problem with a second external monitor. I'm using a 2023 MacBook Pro with M3 chip. It should be able to do this. One monitor is connected with HDMI and other with USBC. I can get either one of them to connect ... but not both. Frustrating!