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My father’s MacBook Pro display is not displaying any image. It happened when he opened the laptop and suddenly the picture was gone. A couple of points. The backlight is working fine and I can adjust the brightness.Connecting the external monitor works.I’ve opened it up twice and disconnected/reconnected the display cables (as far as I know, the right cables). I did not clean the contact pins or anything like that.I’ve tried the reset PRAM/NVRAM and SMC.Starting up in diagnostic mode doesn’t help as it doesn’t work with external displays.I managed to reinstall a clean version of macOS by booting into recovery mode, having the screen open 5-10mm, and squeezing my little finger between the display and touch bar to navigate through the install process, not a fun time. This happened literally a week after the warranty expired. edit - video as requested
Just wanted to be sure. So in your case since the external display is showing an image you’ve isolated out the issue to be with the video signal path vs the backlight as you see the whole display glow grey. Basically the T-CON logic within the display assembly has failed. Sadly the repair requires a new display assembly MacBook Pro 13" Retina (Mid 2018-Mid 2019) Display Assembly and here’s the guide MacBook Pro 13" Two Thunderbolt Ports 2019 Display Assembly Replacement
