Macbook not working with Dock - suggestions?

Issue #1

Your Mac supports a maximum of two external displays.

MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports) - Technical Specifications - Apple Support

Simultaneously supports full native resolution on the built-in display at millions of colors and: 

• One external 6K display with 6016-by-3384 resolution at 60Hz at over a billion colors, or
• One external 5K display with 5120-by-2880 resolution at 60Hz at over a billion colors, or
• Up to two external 4K displays with 4096-by-2304 resolution at 60Hz at millions of colors

Issue #2

Macs do not support driving more than one monitor via a plain USB-C dock, or two monitors via a Thunderbolt one. (Thunderbolt 5 may eventually change the rules, but your Mac doesn't have it, so it isn't applicable here.)

Your Dell dock allows attaching more than two monitors at a time – which means that it drives some outputs in ways that Macs do not support. Please read Dell Support – Knowledge Base – Dell Thunderbolt Docks and Apple USB-C Hosts to learn how to connect two monitors so that each receives a separate signal, allowing the Mac to detect both and allowing you to use extended desktop mode.

markwmsn wrote:

Are these monitors capable of operating as Thunderbolt monitors at all?

Most Dell monitors are not Thunderbolt monitors. They typically accept video in one or more of these forms:

• [Legacy] Single- or dual-link DVI
• HDMI
• DisplayPort
• USB-C (DisplayPort Alt Mode)

The connection between the Mac and the dock is a Thunderbolt one, with up to two DisplayPort signals being carried within the Thunderbolt connection.

The dock has

• A HDMI port
• A DisplayPort
• A USB-C (DisplayPort Alt Mode) port
• A Thunderbolt daisy-chaining port

The first three ports all get copies of the same video signal. So you would plug one monitor into ONE of them; then plug your other monitor (or adapter) into the Thunderbolt daisy-chaining port (from which a display or an adapter would be able to get a USB-C (DisplayPort Alt Mode) signal).

The Mac and the dock would be using Thunderbolt, but the monitors would be unaware that it existed.

"Macbook not working with Dock - suggestions?"

-------

Thank you or the screenshot.

Based on personal experience...

Getting 3 External Displays:

The J5 USB-C Dual HDMI Docking Station allows for more than two extra monitors. How so? Well, plug in a display projector the Macusing the USB-C Digital AV Multiport Adapter and then plug the J5hub with 2 HDMI displays (one 4K), and then you'll have 3 external screens. It all mirrors and extends. It's not officially a third monitor, but you'll get three outputs.

By my reading of the specs on that model MacBook Pro, you are not going to be able to connect three external monitors of any sort; two is the limit. Doesn't even a single external monitor work at any resolution?

Are these monitors capable of operating as Thunderbolt monitors at all?

I'm surprised the HDMI connection by itself doesn't work if the CalDigit TB3 supports it.

Once you have two monitors connected in a proper way, see

Extend or mirror your Mac desktop across multiple displays - Apple Support