Automatic shutdown when there's no external monitor

My MacBook Pro with intel integrated graphics shuts down randomly whenever it is not connected to an external monitor. When connected, either through thunderbolt adapters or HDMI cable, it will run indefinitely without shutting down. However, when I unplug the external monitors it will shutdown within seconds to minutes. If I stream a video while there’s no display connected, I can sometimes get an hour or two of uptime before it shuts down. Does anybody have any clue what could be happening? I’ve reformatted and clean installed Catalina, flashed the NVRAM and SMC, and cleaned the fans and fins.