Type-c monitor MacBook

The external device is acting as a power adapter. IF that device provides ENOUGH power to charge and run at the same time, typically in the neighborhood of 80 watts or higher, there will be enough power to charge and run at the same time. Otherwise, the computer can onlyl charge when the Mac sleeps or is shut down.

The charger is inside the computer. The computer controls when charging begins and ends.

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User have encountered problems when the external device, such as certain Docking devices, does not PROVIDE the full rated power to the computer, but consumes a lot of the advertised power inside the Docking station.

Your computer can use the full output of the Power Adapter AND when doing especially challenging work will also freely "borrow" power from the battery. In some cases, even with the power adapter connected, the charged state may decline during very stressful work.

Power delivery means that the display is providing (UP TO) 90 Watts power for the computer to use, or as little as the computer decides to accept. An external display or power adapter providing power can not 'force itself' on your computer.

The computer only uses as much of that provided power as it wants right now, and ignores the rest. No damage occurs, as ALL the devices are designed to operate this way.

The CHARGER is inside your computer, and your computer only charges (under software control) when measurements of the battery indicate that a charge should be begun.

https://www.lg.com/us/monitors/lg-27up850n-w-4k-uhd-monitor

27" UHD 4K (3840x2160 pixel) monitor with these inputs:

• USB-C (DisplayPort) - also provides 90W USB-C Power Delivery power to a laptop
• DisplayPort
• HDMI

It looks like it comes with a USB-C cable and a DisplayPort cable. If there was some question as to the quality of the USB-C cable – e.g., you saw the Mac cutting the video signal a lot because of transmission errors – you could replace the bundled USB-C cable with another one. (If you got a replacement cable, you would want one rated to carry 4K video and 90W or more of power.)

Hi,

You can connect your MacBook Pro to external monitor via USB-C connection.

Following articles could solve your issue.

Connect one or more external displays with your Mac – Apple Support (AU)

Extend or mirror your Mac desktop across multiple displays – Apple Support (AU)