Also, which laptop is this claim in reference to?
Personal experiences:
13” M1 MBP - one LG 5K display, zero heat or fan speed issues.
16” MBP - I daily drive two LG 5K monitors with no increased heat or fan speed. Prior to picking up the additional LG 5K, I used one LG 5K and two 27” Apple Thunderbolt displays.
15” MBP, with 4 TB3 ports: LG 5K and two 27” Apple TB displays all working without higher heat than w/o them connected
13” MBP, with 4 TB3 ports: same triple monitor setup, same no heat / fan speed issues.
15” rMBP (2015): used two 27” Apple Thunderbolt displays + two 34” ultrawide LG displays, no heat issues or fan issues
The only time I’ve ever seen my laptop stressed by connected monitors is when I did an experiment and connected NINE external displays (ten total screens, as laptop screen was still on) as a test to a 16” MBP to see if it could do it. If I’d had more TB monitors to test with, I think I could’ve done higher count.
Setup in that test:
TB3 port back left: LG 5K display
TB3 port front left: two 27” Apple Thunderbolt monitors daisy chained and using TB3->TB2 adapter
TB3 port back right: eGPU w/ AMD Radeon 580 card connected to two 34” LG ultrawides and two 27” Apple Cinema Display monitors (the older non-TB models)
TB3 port front right: same setup as left, two 27” Apple TB displays
Even then, it definitely wasn’t “overheating”, but processors did idle much higher and fans stayed on during idle (but not at high speed).