So if you have changed the power supply and it’s still doing it it leads me to believe that you have a backlight problem and the only way to fix this is exactly what you are fearing get the brightest light possible or put the tv in a extremely well lit room so during start up it won’t call for the backlight to come on once it powers up go into your settings and turn it all the way down or off
If none of this comes to a resolve then you most likely have burnt row of leds