The reports are disconcerting .
If one uses a 2017 or 2018 MacBook (Pro) as a dual-purpose machine, with an external larger monitor at home, and on its own on the road, then a temperature of 90C is now deemed to be a normal operating temperature when driving a second display, even when the laptop is otherwise just about idle.
In my experience an older MacBook (Pro) is noticeably cooler if it is raised on a stand .
Have you confirmed whether a 2017-2018 MacBook that is connected to an external monitor, and that is otherwise left idle, reports some cooler temperatures?