connect a Mac Pro 3 to external monitors

If this is a MacBook Pro with a plain M3 chip, you can only connect two external monitors – and then, only if you are running macOS 14.6 or later, and the lid of the notebook is closed. With the lid open, the limit is one.

Originally that MacBook Pro could only drive one external monitor. There was latent hardware support for driving a second, "lid closed" monitor, but OS support wasn't ready. So the M3 MacBook Airs got the feature first, and then Apple added it to the plain M3 MacBook Airs via a macOS update.

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

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Note that Macs do not support DisplayPort MST daisy-chaining and do not support connecting two monitors to a "plain" USB-C hub or dock. To drive two monitors with a resolution of up to 4K @ 60 Hz through a hub or dock,

• The Mac has to be capable of driving two monitors
• The dock has to be a Thunderbolt hub or dock

The Mac wants to see a wide Thunderbolt data highway to the dock before it will provide two video signals. If the dock then wants to split the highway into two smaller roads (one for each monitor), that is OK, but there won't be two video signals unless the device immediately connected to the computer is a Thunderbolt one.

A fundamental prerequisite is to identify your specific model Mac, since as others have noted there is no such thing as a "Mac Pro 3".

Identify your Mac Pro model - Apple Support

Identify your MacBook Pro model - Apple Support

Assuming by Mac Pro 3, you mean a MacBook Pro M3 (this is the MacBook Pro forum and a Mac Pro is an entirely different thing) yes, you can connect up to 4 external displays depending on the exact specs of the MacBook Pro.

For regular M3 CPU, you can only connect 1. For one with the M3 Max CPU, you can connect up to 4.

What exact configuration of MacBook Pro do you have?

How are you connecting these monitors to the MacBook Pro exactly?

Are you using a dock or hub? If so, which one?

Are you using adapters? If so which one?

You need to provide details of your setup before anyone can begin to advise.

“connect a Mac Pro 3 to external monitors: Can a Mac Pro 3 connect to external monitors. They are not showing up in my display when I open up in settings”

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External Monitors Not Being Seen in

System Settings:

Confirm the Connection:

See if these are seen in System Information:

1. Go to: Apple menu
2. Hold Down: option key
3. Click: System Information
4. Click: Displays
5. See if they are displayed

If they are not displayed, then they are not being detected. So, a few thoughts in that…

A. Boot in Safe Mode:

In Safe Mode, Login Items do not run at login, certain preferences are set aside, and damaged system files are then reset. So, once booted in to Safe Mode, wait 30 seconds, and try opening it. Then boot up normally, attempting another update install. For instructions, go here: How to Use Safe Mode on your Mac - Apple Support

B. Reset the SMC and your NVRAM:

(Applies to Intel-Based Macs Only): Sometimes when changes are made to the system(i.e. Updates), system configurations (i.e. for Power) become manipulated, technically. So, reset the SMC and NVRAM. Try performing each thrice. It may take sometime, being certain you have the time to perform these resets.