Macbook Pro 2017 Overheating When Using External Monitor

Hi all, I have been having a consistent issue with my 13in MacBook Pro 2017 i5 and wondering if anyone can offer any advice. When using my Dell 27in monitor as an external display connected via USB-C AND using the Mac display simultaneously(ie using the mac keyboard, etc), the Macbook begins to heat up and quickly reaches temperatures >80c. I am not running any high-load software or apps. I don't understand why this is occurring as I thought it was a given that a 2000$ laptop could handle such jobs.

Additionally, and this may or may not be related, after using the MacBook for periods longer than 5-6 hours, dark, flickering lines begin to appear at the bottom of the MacBook display which I have learned is a result of overheating and common on 13inch MBPs. "Poor thermal management leads to the display logic board (T-CON board) getting cooked from overheating. "

Would be great if anyone has any advice or shares a similiar problem.

Thanks