The sound on Disney+ is considerably lower than any other streaming service I use, and I stream a lot. I have to turn the volume up a lot higher whenever I watch anything on Disney+.
I find that HBO Now is also about as quiet as Disney+
Also, lately Disney’s blu-rays have had quieter audio mixes, too. I need to turn their discs up in my home theater about 4 or 5 clicks louder than normal.