I have a Bush (non smart) tv, have you tried turning off energy saving? I always have the backlight set to maximum as well.
You should have access to tv sound/ picture etc settings while in apps, I do if i press and hold 0 for 3 seconds once I'm in the hdmi source. After I got the tv I had to set that up each time but it's finally "stuck" so now it always works.
Alternatively as your TV is a smart tv download the Disney + app and access it that way, see if it makes a difference.