MacBook Pro displays two small screens on one external monitor

What you are looking for is a Thunderbolt 3 or Thunderbolt dock that supports connecting two external monitors with resolutions of up to 4K @ 60 Hz each.

Sometimes docks will bring out video signals on dedicated DisplayPort or HDMI ports.

Sometimes they will have Thunderbolt daisy-chaining ports or Thunderbolt hub ports that are able to support a USB-C (DisplayPort) display or adapter.

A common arrangement is one dedicated video port + the ability to connect another display via USB-C.

If you see a Thunderbolt dock that supports more than two monitors – beware. It probably uses DisplayPort MST daisy-chaining, or the equivalent, internally. Macs don't support that.

If this was a 13” MBP with a plain M1 chip, it would only support one external display. Since ir is a 14” MBP, that implies that it has a M1 Pro or M1 Max chip and supports at least two.

I suspect that the issue is that you are using a plain USB-C dock. Macs only support connecting two displays to a dock when that dock is a Thunderbolt one. The symptoms you are seeing are a bit unusual; most people in your situation just see a mirrored display, or maybe a blank one … not one showing parts of two screens. But if this is a plain USB-C dock, that is the issue.

MacBook Pro (14-inch, 2021) - Technical Specifications - Apple Support

“Simultaneously supports full native resolution on the built-in display at 1 billion colors and:

• Up to two external displays with up to 6K resolution at 60Hz at over a billion colors (M1 Pro) or
• Up to three external displays with up to 6K resolution and one external display with up to 4K resolution at 60Hz at over a billion colors (M1 Max)“

As for a recommended docking station – I don't have a particular docking station in mind, but I would suggest that you consider Thunderbolt docking stations from these three vendors:

Other World Computing

SonnetTech

CalDigit

I do not have personal experience with Thunderbolt docks from any of them – but all three are long-time vendors of high-end Thunderbolt products aimed at Mac users. I believe that in terms of understanding what works well with Macs, and being able to provide good technical support for Mac users, these would be "go-to" vendors you would want to have on your short list.

If you do your own research on their sites (so you can make your questions short and sweet), I assume that any of the three would be happy to answer Mac-related pre-sales questions.

I wouldn't be as sanguine about getting a lot of Mac-related technical support from, say, Dell or HP. They do have some Thunderbolt docks of their own, but for some strange reason, I suspect that supporting Mac customers isn't their top priority …

This article may be interesting.

Other World Computing – Blog – What’s the Difference Between Thunderbolt 3 and Thunderbolt 4?

I had not thought that there would be any disadvantage to buying a Thunderbolt 4 dock or accessory instead of a Thunderbolt 3 one, but apparently OWC thinks that each has advantages and disadvantages, depending upon the way in which your external devices are going to use data.

The article is dated June 20, 2023 – but I just came across it recently, and I learned some things from it that I had not even heard about before, so I thought I'd pass the link along.

Nice article. An explainer written from a user perspective, as opposed to reading the inscrutable specs.

That is really a subtle difference between ThunderBolt-3 and ThunderBolt-4, and I expect we will eventually see inquiries about why user's devices are not as fast as expected.