Concerns over overheating in the EOS R5 and R6 cameras recently emerged. Canon issued a statement to clarify any concerns and explain why design decisions were made as they pertain to the issue.
In the statement, Canon said that the R5's combination of high resolution, high video frame rate, high bit rate, and usage of the full width of the sensor all create a lot of heat. In order to combat this, the company used a magnesium alloy body to help dissipate internally generated heat, along with an "overheat control" function for reducing any heat generation while the camera is in standby mode. In addition to these features, the company also clarified that they decided not to install a fan in the R5 because it would have increased its size and weight and compromised its weather resistance.
The R5 and R6 both contain a rather useful feature that will display the estimated time the camera can record for based on the mode in use and the camera's temperature. The company has also published estimated recording and recovery times for the R5 at an environmental temperate of 73°F (23°C), which you can see below: