Macbook pro 2017 detects wrong external monitor default resolution

SimnW wrote:

• Hi, I have a Lenovo p27u-10 UHD monitor and a MacBook pro 2017 with the latest OS version. When I connect the UHD monitor, it's default resolution detected is FHD (1920x1080) and I have to scale it in system preferences. But with scaling it starts lagging and slows down my Mac.

I tried to connect it via:

Thunderbolt cable from USB-C on the monitor to USB-C on the Mac

• Cable DP on the monitor -> USB-C on Mac

• HDMI-HDMI cable from the monitor to a USB-C hub, connected to Mac

• Normal USB-C-USB-C 3.0 high-speed cable from the monitor to Mac directly

Nothing of that works ok.

However, I have a second QHD monitor Lenovo l24u, which works just fine via HDMI cable connected via a USB-C hub.

How can I make my Mac see the real default UHD resolution on the p27u-10 monitor?

Mirror display also mirrors the display resolution. Extended desktop mode allows you to select the native resolution of the external display.

Try using Extended Desktop Mode instead of Mirror Display Mode.

Get help with video issues on external displays connected to your Mac - Apple Support
 https://support.apple.com/en-us/HT201177