There are no release notes anywhere publicly.
But based on the extensive discussion on avforums.com:
1.) 7.1 LPCM finally works (but the 2020 Samsung TVs still break it... so you have to plug directly into the soundbar)
2.) Game and Adaptive mode both sound better. The center channel distortion is reduced/gone
3.) Many random little things that people griped about (stuff regarding the XSX and Apple TV for example)
I just installed it on the Q70t and my first words were, "holy **bleep**, I think atmos works now". It's a big improvement in the sound quality in my opinion. I felt like the sound never bounced off the ceiling like it was supposed to. Now I can hear the depth in the vertical orientation. In fact, that's why I'm here searching release notes for 1019.5.
Am I crazy?
and does it resolve the sound cuts on Q950T??
I feel so nervous when i´m watching a movie and the sound cuts for a second...it´s very bad for a 1.000€ sound bar...