This is happening as well to me…
Just bought a new MacBook Pro 16'' from 2019 with Radeon 5500M 4 GB.
As soon as it get connected to an external monitor the graphic card just go crazy and start using 18W.
This cause an huge overheating and battery draining super fast. Not able to use the laptop more than 1h if connected to the external monitor, without any other app open and with CPU and RAM at almost 0%. In case the laptop is at 100% and with charger attached, the battery is anyway drained to 95/96%. Unbeliveble!
I tried different monitors (HD, Full-HD, 4k), different HDMI cables and different adaptors. Nothing change.
The issue is there, is quite evident and it's happening to a lot of customers.
I'm honestly quite upset of seeing thousands of people reporting this issue (as well on the AMD support forum) and Apple giving no answers about it. In addition, speaking at the phone with their support center, they were absolutely unable to give me a reply or a solution aside from "ah yeah, the model could have an issue. Return it and you will be refunded."
Is not about fan noise. Is about poor overheating and ridiculous battery life just to connect the laptop to an external monitor.
I'm an Apple customer since 10 years and I never experienced such a poor designed product.
I start a Twitter post to push a bit Apple to pay attention to such huge problem: https://twitter.com/luca_pipolo/status/1303403330673291267?s=20
Please, retweet and like it. Perhaps they will listen to us!