Increased heat on MacBook Pro M4 when connecting multiple external monitors

Based on your other thread, it sounds like you are not experiencing heat when using your M4 Pro MBP but are concerned about heat you may experience if you buy an M4 Pro MBP. If you buy from Apple or an Apple-authorized reseller, you have 14 days to return the Mac no questions asked. My advice is that if you want it, buy it and try it.

Just like my 16" M4 Pro MBP stays nice and cool with the fans off when exporting RAW files, my Mac stays nice and cool while doing that connected to a single 5K:2K display that has the same number of pixels as the combination of three displays you mention.

A 2K display at 10 bits/color uses a stream of data nearly 20 Gigabits/second.

Data must be fetched from RAM memory, serialized, packetized, and transmitted to the display at that ferocious rate. When completed, it must immediately be done again. A refresh rate of 144Hz means you are repainting ALL the data on the display every 144th of a second.

Some additional heat will invariably be generated in the process of doing that very memory intensive operation.

It is expected that the processors will generate more heat as the workload goes up.

Two monitors generate twice the workload.

Your Mac is protected by thermal sensors and will turn on fans, throttle the processors and ultimately shutdown the computer if heat becomes excessive.

Submitted for your perusal:

Important safety information for your Mac - Apple Support (IS)

Keep your Mac laptop within acceptable operating temperatures - Apple Support