Check a Mac Display Limit Before Buying a Multi-Monitor Dock
The number of video sockets on a dock does not establish how many independent displays your Mac supports. Before buying, define the entire display arrangement and compare it with the specification for your exact computer.
Write down the intended combination
Record the complete Mac model and chip, then list each display's resolution and desired refresh rate. Include whether you want to keep the laptop's built-in screen active. Those details matter more than saying that both monitors are “4K capable”.
Look up Apple's display-support page or technical specification for that model. Apple's MacBook Air guidance explicitly ties supported configurations to the model, resolution and refresh rate. It also explains that a supported hub or display chain does not increase the Mac's maximum native display count.
Do not borrow a display-count claim from another Mac that merely has a similar name. Different chip options and generations can have different supported arrangements.
Match the dock to that arrangement
Ask the dock manufacturer whether its advertised combination works with your exact Mac and macOS version. Confirm whether it provides separate extended desktops or duplicates the same image. Check any required driver or software before assuming it behaves like a direct native display connection.
Record the cable and adapter requirements as part of the purchase decision. A display's highest advertised mode is useful only when the entire connection path supports the mode you intend to use.
When testing the new setup, connect one display first, then add the next and inspect Displays settings. Verify that each screen can show a different window, at the intended resolution and refresh rate. Repeat after a normal sleep and wake cycle if that is part of your daily use.
Keep the packaging and compatibility information until those checks pass. A physical connection that lights up two panels is not yet proof that the planned workspace works.
Source: Apple's MacBook Air display-support guidance.
For help with your Mac, contact AEPC in East Auckland or call 027 908 8880 to discuss your requirements.