No such issues here. I’ve got the previous model MBP (2019 15.1", Core i9, Radeon 560X) and it’s not running any hotter or slower than with the previous LG monitor I was using.
Which side of the MBP are you plugging the Spectrum into? Is it the left or the right? MBPs have a notorious issue where charging from the left side USB ports results in the laptop getting a lot hotter, which would kick in cooling and probably thermal throttling. If you use the right side ports, this isn’t an issue.