https://www.techradar.com/news/is-the-macbook-pro-2018-subject-to-excessive-thermal-throttling

Apple’s top-of-the-range 15-inch MacBook Pro 2018 comes with a powerful 6-core Intel Core i9 processor, but a YouTube reviewer has suggested that the device excessively throttles the CPU’s performance when it gets too hot.

Thermal throttling is a rather common practice – it limits the performance of components when they get too hot, protecting the device from damage. The harder a component like a processor works, the more heat it produces.