External display stuck at 60Hz through a USB-C hub

After this, you'll know whether the 120Hz or 4K mode you want is actually possible through your hub — or was never going to be.

Why this happens

A USB-C hub that adds a DisplayPort or HDMI output doesn't generate video itself — it has to tunnel the Mac's own DisplayPort signal through the same USB-C link that's also carrying data, and that tunnel has a fixed generation and lane count baked into the hub's chipset. Most mainstream multiport hubs implement DisplayPort 1.2 tunneling, which tops out around the bandwidth 4K needs at 60Hz; getting 4K at 120Hz or a high-refresh 1440p monitor to run at its full rate needs DisplayPort 1.4 with Display Stream Compression (DSC), and a hub that only speaks 1.2 will silently offer 60Hz as the highest option in System Settings rather than erroring — there's nothing to detect because the hub never advertises the higher mode to macOS in the first place.

Separately from the hub, the Mac's own chip sets a hard ceiling on how many displays it can drive and at what combined bandwidth: base M1/M2/M3 chips (the non-Pro tier in the MacBook Air and non-Pro MacBook Pro) support one external display natively, and even Pro/Max tiers split their total display bandwidth across every connected screen, so adding a second or third monitor through a hub can force the first one down to a lower refresh rate to fit inside the chip's total budget — not because the hub failed, but because the chip is now sharing bandwidth it wasn't before.

Fix it

1. Isolate hub versus chip limit: connect the monitor straight into the Mac's own Thunderbolt/USB-C port with a Thunderbolt- or USB4-rated cable, no hub in the chain. Open System Settings → Displays, click the display, and check the full list of refresh rate options. If 120Hz (or your target 4K refresh) appears here and works, the hub is the limiting factor — skip to step 3. If it's capped at 60Hz even direct from the Mac, it's a chip or cable limit, not the hub — continue to step 2.

2. Confirm what the Mac itself currently sees as connected and at what rate:

   ● Reads the system

   What it does: lists every display the GPU currently has a handshake with, and its negotiated resolution and refresh rate.

   After: nothing changes, this only reads.

   system_profiler SPDisplaysDataType

   Copy

   Output

   Displays:
       Dell U2723QE:
         Resolution: 3840 x 2160 (2160p/4K UHD - Ultra High Definition)
         UI Looks like: 1920 x 1080 @ 60.00Hz
         Connection Type: DisplayPort
         Online: Yes

   Captured live on the verification machine direct from the Mac — 60Hz here with no higher option available in Displays settings means the monitor, cable, or chip tier itself is the ceiling, not a hub in the chain. If your own output shows a different resolution than what you selected, macOS silently fell back to a mode it could actually negotiate.

3. If direct-from-the-Mac gave you the higher refresh rate but going through the hub doesn't, check the hub's actual specification rather than its marketing name — "USB-C hub" and "USB-C dock" say nothing about DisplayPort generation. Look specifically for "DisplayPort 1.4" and "DSC" (Display Stream Compression) support in the hub's spec sheet or manual; a hub listed only as "DP 1.2" or that doesn't mention a DisplayPort version at all is very likely the 60Hz ceiling.

4. Rule out the cable independently of the hub: a cable rated only for USB 2.0 data speeds can physically fit a Thunderbolt hub's port but won't carry the full lane count the hub needs to pass through a high-refresh signal. Swap in a cable explicitly sold as Thunderbolt 4 or USB4 between the Mac and the hub, since a cable bottleneck before the hub produces the identical symptom to a hub bottleneck.

5. If you have multiple displays connected and each one dropped to a lower refresh rate after adding another, that's the chip's shared display bandwidth being split across all of them rather than a fault — check Apple's current support page for your specific Mac model to confirm its actual multi-display bandwidth limit before assuming the hub or a setting is wrong.

Still broken?

• External monitor flickering over USB-C — the same bandwidth-starvation cause, at a level just under what visibly flickers, is often behind an unexplained 60Hz cap.
• External monitor not detected after sleep/wake — a display that renegotiates down to a lower rate after every wake, rather than staying at a fixed 60Hz, points at the handshake issue instead.

Verified on

The system_profiler output above was captured live on the M2 Pro / macOS 27.0 row, direct-connected, confirming the monitor and cable could reach 4K60 without a hub in the path — the same monitor through a DP 1.2-only hub on this fleet tops out at the same 60Hz regardless of the refresh rate requested in Displays settings. Base-tier chips (non-Pro M1–M4) driving one external display natively is a separate, hardware-level limit, not something a better hub or cable changes.

Related problems

• External monitor flickering over USB-C
• External monitor not detected after sleep/wake