Got a similar problem today. Had my X-T4 for a couple of weeks, this is the first time I run in to this.
After an exposure the lcd screen remained black - but clearly powered on, you could see the backlight on the screen.
Powering off the camera and turning it on again did nothing. In the end I took the battery out, not until then the screen shut down entirely and after putting the battery back I could turn on the camera and it worked normally again.
I should add that yesterday I got a new lens (Viltrox 56mm f/1.4). Not sure if it's at all related to the lens or not.