Hello rushabhm,
Thank you for using Apple Support Communities!
We understand from your post that your 29" LG UltraWide Monitor works without issue when using the left-side USB-C ports on your 2018 15" MacBook Pro with TouchBar, but doesn't when using the right-side USB-C ports or the a USB-C to DisplayPort adapter.
MacBook Pro (15-inch, 2018) - Technical Specifications
According to the technical specifications for the 2018 15" MacBook Pro with TouchBar, it "simultaneously supports full native resolution on the built-in display at millions of colors and:
- Up to two displays with 5120-by-2880 resolution at 60Hz at over a billion colors
- Up to four displays with 4096-by-2304 resolution at 60Hz at over a billion colors
Thunderbolt 3 digital video output
- Native DisplayPort output over USB‑C
- VGA, HDMI, DVI, and Thunderbolt 2 output supported using adapters (sold separately)"
Resetting the System Management Controller and/or the NVRAM may help:
How to reset the SMC of your Mac - Apple Support
Reset NVRAM or PRAM on your Mac - Apple Support
The specifications for similar LG UltraWide Monitors show that they support Windows but do not mention macOS. You may want to contact LG to verify if their monitor supports being used on macOS.
Contact Us: Customer Service Phone Numbers | LG USA Support
Best Regards.
