The LG UltraFine 5K Display provides 7.5W to each of its three downstream USB-C (5 Gbps) ports. If you're using this adapter, you need to also connect your Mac to power using the power supply it came with. Power isn't delivered from the display to your Mac when you connect with the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter. The LG UltraFine 5K Display provides up to 85W of power over USB-C and will fully power MacBook Pro (2016 and later) and MacBook Air (Retina, 13-inch, 2018) using the included Thunderbolt 3 (USB-C) cable. With the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter and a Thunderbolt cable, you can use the LG UltraFine 5K Display at 4K and lower resolutions with these Mac models:

You can use the LG UltraFine 5K Display with these Mac models at full 5K resolution: Compatible Mac models are grouped below by the resolutions that they support.

The LG UltraFine 5K Display requires a compatible Mac running macOS Sierra 10.12.1 or later (macOS Sierra 10.12.2 or later is recommended). System requirements and compatible Mac models The display has three downstream USB-C ports (5 Gbps) that offer additional connectivity and power to compatible devices and accessories. When you connect the display using a single Thunderbolt 3 cable (included), it provides up to 85W of charging power to your MacBook Pro with Thunderbolt 3 (USB-C) ports. Integration with macOS lets you control your display's volume and brightness without the need for physical buttons on the display. I usually use a 27' 4K Display by LG with my MBP and have no problems whatsoever (neither over DP nor TB3).The 27-inch LG UltraFine 5K Display features a 5120 x 2880 resolution, a P3 color gamut, 500 cd/m2 of brightness and built-in stereo speakers, camera, and microphone. However, while those work and everything is displayed fluently, the resolution is strongly warped. I am only able to get a picture with my 2018 MBP when I chose a scaled resolution of 1080p or 3840x2160 (for some reason). I also tried a 13' MBP (2020, M1) which works like a charm as does a work laptop from Lenovo (T14). it shifts the controllos to said display and charges when connceted to the TB3-cable).

However, the Macbook correctly identifies the monitor in the system settings and acts as it is supposed to when an external display is connected (i.e. When I try to connect it via a DisplayPort-Cable or via Thunderbolt 3 the monitor doenst get a signal from my Macbook. 13' MBP (2018, 4 Thunderbolt-Ports) issues with Dell U4021QW I just got the Dell U4021QW and am having issues connecting it to my MBP:

Hdmi to mac connector